Lightning Injuries 

Until the last few years, lightning injuries have been the second most common cause of storm-related death in the United States (behind flash floods).^[1] According to data from the National Oceanic and Atmospheric Administration (NOAA), in the years from 1959-1994, lightning was responsible for move than 3,000 deaths and nearly 10,000 casualties. The actual number of lightning casualties may be higher, because up to 50% may go unreported. Lightning kills more people each year in the United States than hurricanes, volcanoes, tornadoes, and earthquakes combined. (See Epidemiology and Etiology.)^[2]

For most thunderstorms, 90% of lightning strikes from cloud to cloud. From 10-30% of lighting can be cloud to ground, depending on the storm. Lightning strikes the earth more than 100 times each second and 8 million times per day. Worldwide, approximately 50,000 thunderstorms occur per day that may result in forest fires, injury to animals and people, and damage to electrical and communications lines and electronics, leading to millions of dollars in downtime for businesses. Since lightning is caused by common meteorological conditions, anyone is a potential victim.

In the United States, cloud-to-ground lightning strikes occur approximately 30 million times each year.^[3] Lightning strikes in the United States are most common in Florida, the Atlantic coast, and along the southeastern coast of the Gulf of Mexico.^[4] The National Weather Service (NWS) estimates that 100,000 thunderstorms occur in the United States each year. Lightning is evident in all thunderstorms. The danger of lightning may not be apparent to an individual because lightning has struck 10 miles away from the rain of a thunderstorm. (See Epidemiology.)^[2]

Lightning starts with short (30-50 m) spurts of static energy in a cloud. The lightning retreats back to its origin, refills the original channel, and branches at the end of the original channel to make a second generation of 30- to 50-m channels. Lightning continues with the retreats and new generations until the charge is either expended (intracloud lightning) or randomly works its way downward as a cloud-to-ground flash.^[5]

Any object under or near the thundercloud will have an opposite charge induced in it, be it a television tower, a tree, a person, or a blade of grass. Multiple upward leaders of current rise from these objects. Most do not contact the main lightning channel but may have sufficient energy to cause injury. Eventually, the downward leader may join 1 or more of the upward streamers to complete the lightning channel. At that point, a return stroke fills all of the branches and the lightning becomes visible.

Only 3 factors predispose to a lightning hit: height of an object, isolation, and "pointiness," which is not a factor with people. However, while lightning has a tendency to hit the tallest object, this 30- to 50-m radius from the last branch point means that tall objects, such as a mountaintop half a mile away, a television tower 300 yards away, a tree 75 yards away, or the goal posts on a football field, are outside the range for protecting anyone (ie, the field's goalposts may not protect someone standing in the middle of a football field if lightning is coming down over the person's head). (See Etiology and Prevention.)^[5]

Although most injuries occur outdoors, a few people are injured indoors every year, including individuals who incur landline telephone-mediated strikes.^{[6, 7]} While use of cell phones, iPods, and other portable electronic devices may change the pathway of lightning around a person, it does not increase the risk of injury except by distracting the individual from paying attention to warning signs, such as storm clouds and thunder.

The most important characteristic features of lightning injuries are multisystem involvement and widely variable severity. This article discusses the physics of lightning and the pathophysiology and treatment of lightning injuries.^[8] Because persons struck by lightning have a better chance of survival than persons who experience cardiopulmonary arrest from other causes, resuscitation for persons struck by lightning must be instituted immediately, followed by a comprehensive treatment program of the other systemic manifestations. (See Prognosis, Presentation, and Treatment.)^[9]

Types of injuries

Injuries range from tiny static electricity ̶ like exposures to cardiac arrest.^{[5, 10, 11, 12, 13]} No good statistics are available for the distribution of severity across the injured population.

Few individuals experience the full energy of a lightning strike because only about 3-5% of injuries are from a direct strike. Most of the energy is mediated by other factors including the ground, the tree, or other object that, once hit, transmits the energy to the person. In fact, less than one third of affected persons have signs of burns. When burns do occur, they are usually superficial.

Internal burns are rare. Myoglobinuria is rarely encountered in lightning injuries, whereas cardiac and respiratory arrest, vascular spasm, neurologic damage, and autonomic instability play a greater role.^[14] Blunt force injuries from falling, being thrown by muscle contractions, or barotrauma from the explosive force of a nearby lightning strike may occur.^[5]

Lightning strikes are primarily a neurologic injury that affects all 3 components of the nervous system: central, autonomic, and peripheral.

Complications

Although rare, serious lightning injuries are likely to primarily cause cardiac and neurologic injury.^{[15, 16, 17]} Otologic injury and cutaneous burns have also been noted as frequent sequelae of these events.^{[16, 18, 19, 20, 21]} Cataract formation resulting from lightning injury typically occurs within days to weeks of injury. This complication has been reported as late as 2 years afterward but commonly occurs within the first week. (See Prognosis, Presentation, Treatment, and Medication.)

Major complications are rare in mild and moderate lightning injuries, although musculoskeletal discomfort and subjective sensations of paresthesias, irritability, and other nonspecific neurologic sequelae may be present, depending on the location and intensity of the strike. In severe lightning injury with cardiopulmonary resuscitation (CPR) required in the field, permanent neurologic deficit and hypoxic injury are common.

Complications of being struck by lightning include the following:

• Chronic pain syndromes
• Neuromuscular pain
• Neurocognitive deficits including short-term memory loss, difficulty accessing or processing new information, attention deficit, personality change, distractibility, or loss of ability to multitask
• Isolation or depression
• Sympathetic nervous system dysfunction
• Dizziness
• Sleep disorders
• Symptoms similar to postconcussion syndrome (eg, headaches, nausea, confusion)
• Atypical seizure disorders

Cardiopulmonary complications include the following:

• Transient hypertension
• Electrocardiographic changes
• Myocardial injury
• Congestive heart failure
• Dysrhythmia
• Transient asystole
• Atrial fibrillation
• Ventricular fibrillation
• Frequent premature ventricular contractions
• Respiratory complications
• Apnea
• Hypoxemia

Damage to the central nervous system (CNS) is the second most debilitating group of lightning injuries.^[22] Neurologic complications include the following:

• Immediate loss of consciousness
• Amnesia and confusion
• Retrograde amnesia
• Hemiplegia, aphasia
• Coma
• Seizures
• Intraventricular hemorrhage
• Hematomas
• Keraunoparalysis

Vascular complications include the following:

• Vasomotor instability
• Arterial spasm
• Vasoconstriction
• Vasodilatation

Ophthalmic complications include the following:

• Cataracts
• Macular holes
• Corneal lesions
• Hyphema
• Iritis
• Vitreous hemorrhage
• Retinal detachment
• Optic nerve injury

Otologic complications include the following^[18] :

• Ruptured tympanic membrane
• Temporary hearing loss

Gastrointestinal (GI) complications of lightning injuries are similar to those following any major trauma.^{[23, 24]} Most common is gastric atony with gastric dilatation, for which placement of a sump nasogastric tube is mandatory to decompress the stomach and remove swallowed air. Another complication seen in victims of lightning injury is GI bleeding, albeit a very rare complication. GI perforation is another rare complication of lightning injury.^{[24, 25]} Buffering the gastric secretions with antacids and administering cimetidine may prevent this. In 2 unusual fatal cases of lightning strike, autopsy findings showed hemorrhage and necrosis in the pancreas.

Classification of lightning injuries

Because a lightning strike can be variable and diffusely spread over the body, most authors characterize lightning injuries as mild, moderate, or severe.

Mild lightning injury is rarely associated with superficial burns, but persons struck often report loss of consciousness, amnesia, confusion, tingling, and numerous other nonspecific symptoms. Lightning burns are invariably superficial and have little or no deep-tissue damaging effects.

Moderate lightning injury may cause seizures, respiratory arrest, or cardiac standstill, which spontaneously resolves with resumption of normal cardiac activity. Much of the symptomatology mirrors that of mild lightning injury, except superficial burns are much more common, both initially and in a delayed fashion. These patients may have lifelong symptoms of irritability, sleep disorders, and paresthesias.

Patients with severe lightning injury usually present with cardiopulmonary arrest, which is often complicated by a prolonged period in which they did not receive CPR. This delay is attributable to the fact that these individuals are often in an isolated location when injured. Survival is rare in this group unless a bystander expeditiously begins CPR.

Physics of lightning

Lightning is a natural atmospheric electrical discharge that occurs between regions of net positive and net negative electrical charges. Usually, it is associated with cumulonimbus (thunder) clouds, but it may occur in nimbostratus clouds, snowstorms, or in the erupting gas of an active volcano. A complex sequence of events leads to a lightning discharge in a thunderstorm.

Updrafts of air drawing moisture from the upper atmosphere result in rapid cooling and formation of ice particles. Complex updrafts and downdrafts associated with storm formation cause these particles to collide rapidly, building up static electrical energy. A net positive charge develops in the upper levels of the clouds at an altitude of approximately 10 km and a temperature of about -45°C. Subsequently, a net negative charge develops in the lower levels of the clouds at an altitude of approximately 5 km and a temperature of about -15°C. Although the earth is usually negatively charged, an area of positive charge exists 2 km beneath the storm cloud (+5°C). When the potential difference exceeds the insulating properties of air, a lightning flash occurs.

Streak lightning

A flash of cloud-to-ground streak lightning is initiated by an electrical breakdown between the positive and negative charge regions. A faint, luminous process descends in regular steps (typically 50 m long at intervals of 0.05 ms in a downward, branching fashion toward the ground). This initial flow of electricity, the leader stroke, reaches the ground in approximately 20 ms. The diameter of the stepped leader ranges from a few centimeters to a few meters, depending on what parameter is measured. Within the leader is a current-carrying core 1-2 cm in diameter.

As the branching process nears the ground, an upward discharge, termed the upward streamer, completes the path of ionization approximately 30-50 m above the surface of the earth. At this moment of junction, the cloud is short-circuited to the ground, and the major electrical discharge, a luminous return stroke of high current, occurs. Following the initial stroke, secondary leader and return strokes frequently occur. Lightning tends to strike tall objects because, although the earth‘s normal electrical field runs in equipotential planes parallel to its surface, these planes are elevated over trees, hills, and tall buildings.

Lightning is seen moving only from cloud to earth because the energy needed to ionize the air is so great that it is the brightest portion of the strike (usually the downward leader is too weak to see). Furthermore, its relatively slow speed (1-2 x 106 m/sec) in reaching the earth makes it easier to see. The extreme speed (2-5 x 107 m/sec) of the return stroke prevents its visualization, yet it may be perceived as an instantaneous brightening or pulsing of the pathway. The upstroke reaches the cloud base in 0.07 ms, while the downward-propagating stepped leader traverses the same distance in 20 ms.

Thunder

Air that is crossed by lightning is heated rapidly, and the cylindrical column expands at supersonic speeds. Within 1 or 2 meters, the shock wave decays to a sound wave, thunder, which comes from the entire channel length, producing a series of sounds described as peals, claps, rolls, and rumbles. Because light travels at 186,000 miles/sec and sound travels at 1100 ft/sec, the time elapsed between the flash and thunder permits calculation of the minimum distance to the flash. Duration of the rumble provides the minimum estimate of the length of the air channel; however, thunder rarely is heard at distances greater than 15 miles because of such factors as terrain, atmospheric temperature, and wind shear.

The power of lightning is awesome, an estimated 10,000-200,000 amperes (A) of current and 20 million to 1 billion volts. A current of 100,000 A can shift blocks of stone weighing 5 tons, and rocks weighing 50 pounds may be thrown 20 yards or more.

Types of lightning

Streak lightning, described earlier, is the most frequent type of lightning and accounts for human injuries. Another type, sheet lightning, travels within a cloud and gives the cloud the appearance of a white sheet. Several rare forms of lightning are ribbon and bead lightning. These are forms of ground discharge with a flash consisting of several strokes. Ribbon lightning occurs when the channel is blown perpendicular to the line of sight by the wind, displacing subsequent strokes. Consequently, the flash appears as a ribbon of several strokes. In bead lightning, the main lightning flash breaks into luminous sections, or beads, as the light intensity of the channel decays.

The most rare and mysterious form of lightning is ball lightning.^[26] A mix of fire and electricity concentrated in a fireball with a diameter of 20 cm, ball lightning commonly appears suddenly, even in indoor conditions, during a thunderstorm. It moves quickly for several meters, can change direction, and ultimately disappears. It has a life span of several seconds, and its color is quite variable. Ball lightning often results in an explosion.

On rare occasions, passengers and crews have witnessed ball lightning traveling down the center of an airplane.^[27] These glowing balls of electrical energy have been reported to dissipate quietly at the rear of the airplane or to exit with a loud bang, leaving residual burn marks on the interior of the plane. These differing final exits may be related to the range of the energy content of the glowing balls. Cherington et al reported a coronal discharge and ball lightning–induced injury to a flight attendant on an airplane.^[27] As a result of this lightning-related event, the flight attendant sustained a demyelinating injury of the brain, the symptoms of which resolved after 22 months.

Patient education

Patient resources include the following:

• Lightning Strike and Electric Shock Survivors International- Phone: (910) 346-4708; e-mail:info@lightning-strike.org
• Lightning Injury Research Program
• Lightning Safety
• Struckbylightning.org

For patient education information, see Lightning Strike.

Lightning can be considered the ultimate in cosmic cardioversion, producing atrial and ventricular arrhythmias, myocardial injury, and vasomotor responses.^[28]

The direct current of lightning depolarizes the entire myocardium at once, causing a single systolic contraction followed by a variable period of asystole (primary cardiac arrest). Cardiac activity may return spontaneously, first at a markedly bradycardic rate and then slowly increasing in speed. Rhythm may deteriorate from apnea resulting from paralysis of the respiratory center in the medulla. Development of hypoxia leads to secondary cardiac arrest with ventricular fibrillation.

Lightning injuries versus common electrical injuries

Although lightning injuries are related to common electrical injuries, the physics of lightning is far different, leading to significant differences in the pathophysiology and injury patterns, and these factors must be considered to provide the best possible care to persons with lightning injuries.^[29]

Lightning cannot be classified as either direct current or alternating current. Lightning is not "scalable"—one cannot use their experience and knowledge of 110-volt lines or high-voltage injuries to predict what lightning will do. The physics of lightning is incredibly complex and substantially different from the physics of generated electricity.

It should be remembered that the vast majority of lightning injuries are from indirect mechanisms; the following explanation applies only to direct strikes. Probably the most important difference between lightning and high-voltage electrical injuries is the duration of exposure to the current, which also affects the path it takes. While the energy from lightning may flow through the person for an incredibly brief period (4-6 msec), usually the vast majority of lightning energy flashes around the person's body surface.^[30]

Lightning has only brief contact with skin, and, in most instances, the contact is too brief to burn the skin substantially. Entry and exit are inappropriate terms to apply to lightning injuries.^[5] In addition, because of this “flashover” effect by lightning, myoglobinuria, renal failure, and compartment syndrome occur much more rarely from lightning injury than from commercial electrical injury.

Lightning also has a shock wave component that can cause injury.^[31]

When current does enter the body, almost every organ system is vulnerable. A wide variety of complications can result from damage to these organ systems, and specific sequelae dictate the choice of therapy.

Although it is often not possible to document which mechanism of lightning injury was involved in a particular case, such knowledge does not influence patient care.

Types of human lightning strikes

Lightning may injure an individual in 6 ways.^{[5, 32, 33, 34]}

• Direct strike (approximately 3-5% of injuries)
• Side splash from another object (approximately 30% of injuries)
• Contact voltage from touching an object that is struck (approximately 1-2% of injuries)
• Ground current effect as the energy spreads out across the surface of the earth when lightning hits a distance away from the person (approximately 40-50% of injuries)
• Upward leader that does not connect with the downward leader to complete a lightning channel (approximately 20-25% of injuries)
• Blunt trauma if a person is thrown and barotrauma from being close enough to experience the explosive force of lightning^[31]

Direct strikes occur to victims who are outside. Although not always fatal, direct strikes are associated with high morbidity because they frequently involve the head. Lightning strikes near the head may enter the eyes, ears, and mouth to cause multiple problems.

More commonly, the victim is struck by a flash discharge from another struck object. This type of splash injury occurs, for example, when someone seeks shelter beneath a tree, picnic shelter, or other object that is struck by lightning. A portion of the lightning may jump from the object struck to the victim. Splash injury also occurs from person to person when several people are standing close together.

Contact injury occurs when a person is touching an object that is either directly hit or splashed by lightning, such as indoor plumbing or wiring, hard-wired phones, a metal fence, bleachers, or other objects struck by the lightning.

Lightning also can result in harmful ground current that causes mass casualties in fields or other open areas. Severity of ground current injuries decreases with distance from the point of the lightning strike.

Energy sufficient to cause death or injury also occurs in an upward streamer that can be induced in a person near a thunderstorm.^[33]

Blunt trauma occurs when a person is thrown by a massive opisthotonic contraction caused by the lightning strike. A new report also documents internal injury from blast effect.^[31]

Risk factors

The primary risk factor for lightning injury is the failure to acknowledge that lightning poses a threat. Lightning safety and injury prevention is not convenient. It involves being aware of weather predictions, sometimes changing plans, and proactively planning evacuation to safer areas and the time to reach them. No place outside is safe when thunderstorms are in the area.^{[13, 35, 36, 37, 38]}

Lack of knowledge of lightning danger and the mechanisms of injury also contribute to the risk. Many people try to finish one more inning or wait until rain begins before seeking shelter. This is often too late because lightning can travel as far as 10 miles in any direction from the thunderstorm clouds. The interstrike distance, depending on the local terrain and geography, may be as far as 5 ±5 miles, for a range of 0-10 miles (and sometimes more) from the last stroke.

Despite popular belief, nothing attracts lightning. The primary physical factors that make an object statistically more likely to be struck are isolation, height, and narrowness of the tip of the object facing the cloud. Only the first 2 factors apply to people.

While lightning can be seen hundreds of miles away on the Great Plains or not at all in heavily forested areas, thunder usually cannot be heard more than about 10 miles away. By the time one hears thunder one is already in danger and should be seeking shelter or seeking a safer shelter. "When thunder roars, go indoors!" is the theme taught to children for injury prevention and is the theme of National Lightning Safety Awareness Week.

The only reason that cell phones and iPods are dangerous in thunderstorms is that they distract the individual from paying attention to the weather and hearing thunder, the primary warning signal for lightning. Although it is theorized that they may change the pathway of the lightning once a person is injured, they do not attract lightning.

Although lightning injuries during recreational activities tend to predominate in industrialized countries, nearly one third of US lightning injuries are work-related, on-the-job injuries. In less developed, more labor-intense agrarian societies, the proportion of work-related injuries and deaths is probably higher.^[39] In addition, a small number of injuries occur inside structures every year.

Certain geographic areas are more prone to lightning, such as mountains, parts of Florida and the Gulf Coast, the Eastern Seaboard, and the major river valley areas of the Midwest because of weather patterns, moisture content of the air, and updrafts.

Indoor exposures

In general, being inside a substantial, habitable building such as a house, library, or school is one of the safer areas to seek shelter. The increased safety is credited, in part, to the fact that these structures tend to have plumbing and wiring in them, acting as a Faraday cage to transmit any electricity around the inhabitants.^{[35, 36, 37, 38]}

Unfortunately, it is also true that lightning may hit or hit near a structure or recreational facility and be transmitted into the building through the plumbing, electrical wiring, emergency medical service (EMS) or fire dispatch radio, or other routes. This includes facilities with indoor pools, which should be evacuated using the same rules as outdoor pools. Individuals should avoid touching plumbing or objects that are electrically hard-wired to the structure's electrical system including telephones, computers, and electronic games wired to televisions and computers.

Taking shelter in any structure that includes the word shelter (eg, bus shelter, sun shelter, park shelter, golf shelter, rain shelter) generally provides no protection. To date, national lightning-protection building codes (National Fire Protection Association: NFPA 780) address only physical protection of shelters but not for people using them. Many believe that these structures may substantially increase the risk of lightning injury by increasing the functional height of the individuals standing under them, by increasing the risk of a side flash or ground current from a transmitted strike in structures with a lightning protection system, or by other mechanisms too long to go into in this discussion.

Being inside a fully enclosed metal vehicle is a very safe place due to the fact that electricity will flow along the outside of any metal structure that it hits, not due to the miniscule effect of rubber composite tires. While being inside a vehicle when it is hit has been likened to "being inside a garbage can where someone threw two cherry bombs" and may be quite unpleasant, there has never been a substantiated electrical injury to a person inside a vehicle unless that person was touching a handheld radio hard-wired to the car’s antennas or some similar connection to the outside.

Telephone injuries

Hard-wired telephones become the conduit for the lightning charge to enter or to escape from a structure (and the person).^[7] Although the telephone system may be grounded adequately for electrical surge protection, lightning energy surge is much too fast and strong for typical grounding and surge protection systems to be effective and reaches the person before the circuit breaker or other protection can be effective.

Injuries to persons using telephones or telephone headsets, such as those who take phone orders, used to be common but have decreased substantially now that wireless systems are more in use.

Older, portable phones, seldom used now in the United States, were a rare source of lightning injury to people standing within a yard or so of the base station or charger. Those injuries were caused by the lightning jumping from the charger to anything close by and had little to do with the phone the person was carrying.

No lightning danger is inherent to cellular phones. Although many reports of lightning injuries involve people who are using cellphones, these reports represent the ubiquity of cellphone usage and of their users' inattentiveness to weather conditions and have nothing to do with the phones themselves.

In the past, acoustic injury was possible from the loud static noise in the earpiece of early portable phones, but to date, acoustic damage involving cellular phones has not been reported.^[7]

Thunderstorms and lightning are most common from June through September. Lightning strikes usually occur in the afternoon and evening, coinciding with times when people are active and outdoors. Hikers, campers, and other outdoor sports enthusiasts most often sustain lightning injuries. Lightning injuries are more common in rural or exposed environments than in the city, where high buildings have metal frames and lightning-protection devices. In the past 3 years, the majority of deaths have been to individuals who were within a few feet of safety and doing routine things, including mowing the lawn or going outside of a store to get better phone reception.^[40]

Lightning may strike as far as 10 miles in any direction from a thunderstorm, before the rain starts, or while the sky above is still clear. At least 10% of lightning hits when blue sky is visible.^{[36, 37, 38, 41]} The most dangerous times for lightning injury are when the person underestimates the likelihood of being hit (ie, before the storm or at the apparent end of the storm).

Occurrence in the United States

For the past 40 years, lightning has consistently been the second largest storm-related killer in the United States,^[42] with 45-50 persons killed annually by lightning. From 2000-2006, the estimated annual rate of deaths attributed to lightning strikes was 0.2 per million people.^{[40, 43, 44]}

However, sources of lightning injury data (the National Center for Health Statistics and Storm Data) systematically underestimate the number of fatalities by 28-42%.^{[5, 45]} One reason is that much of the older data are taken from newspaper accounts using clipping services to catch them, so if people struck by lightning do not make the news, they are not entered into the statistics. Newspaper reports have been a major source of national statistics on lightning deaths for many years. In the last 6 years, search engines such as Google have replaced clipping services for collection of lightning fatality data by the National Climate Data Center’s (NCDC’s) Storm Data and Lightning Safety Week (LSW) committee.^[40]

Most survivors of lightning strikes do not need to be admitted to a hospital and, as a result, do not show up in medical data banks. Moreover, many survivors do not seek immediate medical care and only come to the attention of medical personnel when they seek care for effects of the shock that have not resolved within a few days after their injury. Because injuries are so infrequently reported compared with fatalities, a rule of thumb developed from many studies is that injuries occur about 10 times more often than fatalities do.

Most injuries occur between May and September. The National Center for Health Statistics has documented that the majority of US deaths by lightning strike occur in the South and the Midwest, with Florida and Texas leading the list.^{[40, 44]}

In 2005, Adekoya and Nolte used data from both the National Centers for Health Statistics (NCHS) multiple-cause-of-death tapes and the Census of Fatal Occupational Injuries (CFOI), which is maintained by the US Bureau of Labor Statistics, to investigate the epidemiologic characteristics and annualized rates of lightning-related deaths for the United States.^[44]

From 1993-2000, 374 struck-by-lightning deaths were recorded, for an average annualized rate of 0.23 deaths per million persons. Incidents in the South and the Midwest accounted for the majority of fatalities (286 deaths, 75%; with the greatest number of deaths in Florida [49 deaths] and Texas [32 deaths]). From 1995-2002, 1 of every 4 struck-by-lightning deaths was work-related (129 deaths; average annual rate of 0.12 deaths per million workers), with agriculture and construction industries accounting for the most fatalities at 44 and 39 deaths, respectively. Fatal occupational injuries were greatest in Florida (21 deaths) and Texas (11 deaths). As found in many other studies, incidence rates were higher for males and people aged 20-44 years.^[44]

Almost all prior studies have looked at lightning injuries per state and not by geographic features or population centers. A novel and interesting study by Ashley and Gilson mapped deaths from 1959-2000 reported from multiple databases by location of occurrence to create a spatial map.^[46]

The map revealed an urban theme with high fatality counts clustered along population centers and lower counts scattered across rural areas. The highest counts were noted along central and eastern Florida and a corridor paralleling Interstate Highway 95 from Washington DC, Baltimore, Philadelphia, and New York City. Overall, metropolitan areas in Florida showed the highest counts, the New York/Atlantic area the second, and the Chicago area the third highest clusters. In returning to a state analysis, when adjusted for area, 4 of the top 5 normalized fatality rankings by state were in the Mid Atlantic and Northeast, with Florida being the fifth state in the count.^[46]

Another way to cluster injuries and direct prevention strategies is by looking at where the greatest number of thunderstorms occur the South; Rocky Mountain area; Gulf and Atlantic Coasts; and the Ohio, Mississippi, and Hudson River valleys.

Obviously, injury prevention efforts should be maximized in the areas of most historical risk, while at the same time being watchful of changing patterns. Specialized risk areas such as wilderness recreation and water have not been analyzed by population and other tight epidemiologic methods but seem to pose high risk based on viewing of the data and newspaper reports.

The most common days of injury in the United States are Saturdays and Sundays, probably reflecting the recreational activities on the weekends. The most common time of day to be injured by lightning is from noon to 6 pm, with 6 pm to midnight following, related to not only when thunderstorms occur but also to when people are most likely to be outdoors.^{[5, 40, 47]}

International occurrence

Compiling and recording statistics internationally is a challenge because of the lack of a good reporting system.^[48]

Lightning is much more common near the equator. Total annual fatalities are estimated to be about 24,000, and annual injuries are estimated to be about 240,000 for the tropical and subtropical areas of the world, where lightning is most common and the economies tend to be more subsistent, agrarian, and labor intensive than they are in the more developed and temperate climates.^{[5, 43]} In general, lightning injuries and deaths decrease in any country as the economic system, urbanization, and housing improve, not only because direct numbers of persons exposed to lightning decreases but also because housing that contains plumbing and wiring provides substantial protection.^[49]

Race-, sex-, and age-related demographics

No direct relationship to race is known to exist. An indirect relationship may be present based on employment or recreational activities.

In a US study, data from 1959-1994 indicated that males were 4.6 times more likely to be killed and 5.3 times more likely to be injured by lightning than were females. This was not because of any physiologic differences but was considered to be a consequence of males' increased exposure to potential lightning-strike situations, such as outdoor activities or work, as well as probably to males’ higher level of risk-taking behaviors.^{[5, 40]}

Of deaths and injuries, 85% occur to persons aged 10-59 years. Few adults older than 60 years are injured. This is probably related to the decreased chances of exposure of this age group during outdoor recreation or employment.^{[5, 40]}

Overall, patients' outcomes and prognoses after most lightning strikes are good. Unfortunately, many individuals struck by lightning have permanent disabilities. In patients who have endured a severe strike, the potential for permanent and debilitating neurologic and cardiac injury is greater.

However, no good long-term, controlled studies are available to indicate if lightning-related injuries improve or progress to more serious disabilities or to give stratified prognoses for different subgroups of survivors. As with other injuries, the longer a person has a symptom or sign, the more likely each is to be permanent.

Morbidity and mortality

Lightning causes death in about 10% of its victims.^[45] Death from lightning injury is unrelated to sex, age, and the presence of trunk and arm burns. Factors that appear related to a fatal outcome are leg burns, head burns, and immediate cardiopulmonary arrest.^[19] Some reports suggest as many as 74% of survivors of a lightning strike experience permanent injury and sequelae.^[19] Other studies suggest the percentage with permanent injury is less; however, there continues to be controversy over the long-term effects in general.

Most lightning-associated deaths are caused by cardiac arrest.^{[15, 16, 17]} Forensic physicians must also consider lightning strike in the differential diagnosis of sudden unexpected death in persons found outside.^{[50, 51, 52]} The most common minor injury reported is rupture of the tympanic membranes.^[53] Superficial burns and eye injuries are the most frequently reported injuries.^{[16, 19, 20, 21]} The most common chronic sequelae reported are brain injury and chronic pain syndromes.

Lightning injuries differ from those resulting from high-voltage direct current because lightning injuries usually do not cause significant tissue destruction along the path of grounding of the current. Lightning strikes are usually diffuse and do not commonly cause injuries similar to those received from 110-volt (V) or 220-V electrical currents. Blunt physical injury may also accompany lightning injuries; therefore, medical personnel should also screen lightning victims for occult blunt trauma.^[16]

Neuropsychological sequelae of lightning injury can cause significant morbidity.^[22] Survivors of lightning injury report heightened anxiety states, hyperirritability, memory deficits, aphasia, sleep disturbance, attention deficit, deficits in working memory, and posttraumatic stress disorder.^{[54, 55]} These symptoms also are found in patients with blunt head trauma, yet the sleep disturbance and memory difficulties are more severe than those caused by blunt brain injury.

Lightning injury is a neurologic injury, affecting all 3 parts of the nervous system, as follows^{[56, 57, 58, 59, 35, 60, 61, 62, 63]} :

• Brain - Neurocognitive changes, sleep disturbance, personality change, seizures, learning disability, postconcussive-type headaches, nausea, attention deficit, distractibility, vestibular injury
• Autonomic nervous system - Regulation of blood pressure and cardiac response (positive tilt test results, dizziness, hypertension), GI insult, impotence, sympathetically mediated pain syndromes
• Peripheral nervous system - Chronic pain, sensory problems

Most patients with injuries caused by lightning regain consciousness. However, more than half of all patients injured by lightning experience transient motor paralysis (69% incidence of paralysis of the upper extremities and 30% incidence of paralysis of the lower extremities), usually sparing the ventilatory center. Paralysis from lightning injury is known as keraunoparalysis and is associated with sensory loss and cyanosis. Total resolution of paralysis usually occurs in minutes to days. If paralysis does not improve, other causes, such as direct spinal cord injury or blunt injury from a fall, should be suspected.