Postconcussive syndrome (PCS), a sequela of minor head injury (MHI), has been a much-debated topic. Muddled by conflicting findings regarding symptom duration, an absence of objective neurologic findings, inconsistencies in presentation, poorly understood etiology, and significant methodologic problems in the literature, postconcussive syndrome (PCS) remains controversial. Depending on the definition and the population examined, 29-90% of patients experience postconcussive symptoms shortly after the traumatic insult. [1, 2, 3, 4]
See Pediatric Concussion and Other Traumatic Brain Injuries, a Critical Images slideshow, to help identify the signs and symptoms of TBI, determine the type and severity of injury, and initiate appropriate treatment.
Minor head injury and concussion are generally used interchangeably in the medical literature; however, it should be noted that the traditional definition of concussion precludes findings of intracranial hemorrhage on CT scan, whereas the definition minor head injury does not (though it does preclude the presence of a skull fracture). A minor head injury typically indicates a blow to the head with a brief period of loss of consciousness (LOC) or posttraumatic amnesia or disorientation. At presentation, the Glasgow Coma Scale (GCS) score ranges from 13-15. However, more recent literature suggests, and many clinicians concur, that a GCS score of 14 or 15 denotes an injury with a significantly less chance of intracranial injury on CT scan than a GCS score of 13.
Although no universally accepted definition of postconcussive syndrome exists, most of the literature defines the syndrome as the development of at least 3 of the following symptoms: headache, dizziness, fatigue, irritability, impaired memory and concentration, insomnia, and lowered tolerance for noise and light. Confusion exists in the literature, with some authors defining it as symptoms of at least 3 months' duration, while others define it as symptoms appearing within the first week. In this article, the syndrome is loosely defined as symptom occurrence and persistence within several weeks after the initial insult. Persistent postconcussive syndrome (PPCS) is generally defined as symptoms lasting more than 6 months, though some authors define it as symptoms lasting more than 3 months.
In a study of patients aged 5 to younger than 18 years who presented with acute head injury in pediatric emergency departments, 801 of 2584 patients (31%) experienced PPCS, or acute concussion followed by ongoing somatic, cognitive, and psychological or behavioral symptoms. 
The ICD-10 criteria include a history of traumatic brain injury (TBI) and the presence of 3 or more of the following 8 symptoms: (1) headache, (2) dizziness, (3) fatigue, (4) irritability, (5) insomnia, (6) concentration or (7) memory difficulty, and (8) intolerance of stress, emotion, or alcohol.
According to the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), postconcussive syndrome is given a diagnosis of either major or mild neurocognitive disorder (NCD) due to TBI.  The DSM-5 criteria for neurocognitive disorder due to TBI include the following:
Evidence of traumatic brain injury: impact to the head or other mechanisms of rapid movement or displacement of the brain within the skull with any of the following: loss of consciousness, posttraumatic amnesia, disorientation and confusion, neurologic signs such as new onset of seizures, anosmia, or hemiparesis.
The neurocognitive disorder presents immediately after the occurrence of the TBI or immediately after recovery of consciousness and persists past the acute post-injury period.
Debate in the literature exists over which symptoms of postconcussive syndrome are due to organic causes and which have a psychological basis. Researchers have hypothesized that early postconcussive syndrome symptoms are more likely to be organic, whereas postconcussive syndrome symptoms that persist beyond 3 months have a nonorganic, psychological basis. While recent research has shown that psychological factors may be present early, other studies using imaging techniques such as magnetic resonance imaging (MRI), single-photon emission computed tomography (SPECT), and magnetoencephalography (MEG) have demonstrated the presence of organic brain injury in patients with persistent postconcussive syndrome at greater than 1 year after injury.
Neuropsychological assessments have pointed toward an organic basis for some of the symptoms of postconcussive syndrome. Patients with PCS have been found to have cognitive deficits in memory, attention, and learning when compared with controls. A prospective study found impaired eye movements in patients with PCS, as compared to controls, that were both persistent and independent of factors such as depression or intellectual ability.  Findings from neuropsychological evaluations demonstrate that symptom severity is not necessarily dependent on neurologic status immediately following injury. However, in other series, the length of LOC or posttraumatic amnesia may be correlated with the probability of developing postconcussive syndrome.
Some studies have found certain characteristics such as female sex, noise sensitivity, and anxiety predict development of symptoms.  Another study found a simple test in the ED of immediate and delayed memory for 5 words and a VAS for acute headache provided an 80% sensitivity and 76% specificity for the development of PCS.  In addition, another study found that higher educational levels, along with mild symptoms and no extracranial symptoms predicted a low likelihood of significant dysfunction from PCS.
More than 1 million instances of minor head injury occur in the United States each year. The overall incidence rate of minor head injury for persons not hospitalized, with data compiled by the National Hospital Ambulatory Medical Care Survey, was 503 per 100,000 population or 1,367,101 visits per year to hospital EDs in the United States.  Depending on the definitions used and population examined, approximately 50% of patients with minor head injury have symptoms of postconcussive syndrome at 1 month and 15% have symptoms at 1 year. The number of patients who sustain minor head injury and do not present for medical care is unknown, therefore the number of patients with postconcussive syndrome is likely significantly underdiagnosed.
Morbidity is mainly due to the persistence of symptoms, which make it difficult for patients to resume premorbid functions. Between 14 and 29% of children with mild traumatic brain injury will continue to have postconcussion symptoms at 3 months. 
Men experience minor head injury more frequently than women, but the incidence of postconcussive syndrome is greater in females than in males.
True prognosis is difficult to define given that many patients with minor symptoms may not enter the health care system and those that participate in research appear to have more significant symptoms at baseline. In addition, a wide heterogeneity exists in patients enrolled in studies.
Most patients recover fully in less than 3 months, although some small studies suggest persistence of minor cognitive defects for asymptomatic minor traumatic brain injury patients. 
Approximately 15% of patients complain of problems more than 12 months after injury. This group is likely to experience persistent and intrusive symptoms that may be refractory to treatment and impose a lifelong disability.
At least one study found the persistence of dizziness as a symptom seemed to portend a longer and more significant symptom complex.  Other studies found the depression, pain, and symptom invalidity were correlated with longer and worse symptoms.  Another found patients with early clinical symptoms, such as headache, dizziness, and intracranial lesions were more likely to have persistent PCS.
PCS is commonly associated with multiple concussios, but in one series, 23.1% of patients experienced PCS after only 1 concussion (average was 3.3 concussions). Median duration of symptoms in this series was 7 months. 
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