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      Drugs & Diseases > Neurology

      Mercury Toxicity Clinical Presentation

      Updated: Nov 05, 2018
      • Author: David A Olson, MD; Chief Editor: Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS  more...
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      Presentation

      History

      The diagnostic approach for patients with suspected mercury toxicity begins with a thorough history that includes occupations, hobbies, and levels of seafood intake. All toxic presentations, whether acute, chronic, or subacute, are difficult diagnoses because multiple organ systems are affected (eg, CNS, kidney, mucous membranes) and can mimic a variety of other diseases. If no such history exists, clinical suspicion can be confirmed by laboratory analysis.

      The symptoms of mercury intoxication are manifold. Patients can present with complaints of numbness, tingling, hearing loss, visual difficulties, gait unsteadiness, and tremulousness, as well as emotional and cognitive difficulties. Obviously, assessing the risk of exposure, which can be acute or long term, is paramount to making a diagnosis.

      Some unique features of mercury poisoning have generated their own nomenclature, as follows:

      • Metal fume fever - Occurs in the acute phase of mercury vapor toxicity and is manifested by fatigue, weakness, fever, chills, dizziness, headache, abdominal cramping, dyspnea, dysuria, and ejaculatory pain

      • Acrodynia - Also known as pink disease and considered to be a mercury allergy; presents with erythema of the palms and soles, edema of the hands and feet, desquamating rash, hair loss, pruritus, diaphoresis, tachycardia, hypertension, photophobia, irritability, anorexia, insomnia, poor muscle tone, and constipation or diarrhea; acrodynia does not present in everyone who is exposed to inorganic mercury, but it is an indicator of widespread disease [62, 63]

      • Erethism - A constellation of irritability, excitability, anxiety, insomnia, and social withdrawal; erethism traditionally is seen in the chronic phase of the inorganic mercury toxicity.

      Chronic and intense, acute mercury exposure cause cutaneous and neurologic symptoms. The classic triad found in chronic toxicity is tremors, gingivitis, and erethism. Additional findings may include headache, visual disturbance (eg, tunnel vision), peripheral neuropathy, salivation, insomnia, and ataxia.

      Inorganic mercury exposure

      Exposure to inorganic mercury or mercuric salt occurs mainly through the oral and GI tract. Its corrosive properties account for most of the acute signs and symptoms of inorganic mercury or mercuric salt toxicity. The acute presentation can include ashen-gray mucous membranes secondary to precipitation of mercuric salts, hematochezia, vomiting, severe abdominal pain, and hypovolemic shock.

      Systemic effects usually begin several hours postingestion and may last several days. These effects include metallic taste, stomatitis, gingival irritation, foul breath, loosening of teeth, and renal tubular necrosis leading to oliguria or anuria.

      Organic mercury exposure

      Organic mercury poisoning usually results from ingestion of contaminated food. The long-chain and aryl forms of organic mercury have similar toxic characteristics as inorganic mercury. The onset of symptoms usually is delayed (days to weeks) after exposure.

      Organic mercury targets enzymes, and the depletion of these enzymes must occur before the onset of symptoms.

      Symptoms related to toxicity are typically neurologic, such as the following:

      • Visual disturbance - Eg, scotomata, visual field constriction

      • Ataxia

      • Paresthesias (early signs)

      • Hearing loss

      • Dysarthria

      • Mental deterioration

      • Muscle tremor

      • Movement disorders

      • Paralysis and death - With severe exposure

      Organic mercury targets specific sites in the brain, including the cerebral cortex (especially the visual cortex), motor and sensory centers (precentral and postcentral cortex), the auditory center (temporal cortex), and the cerebellum.

      If methyl mercury intoxication is suspected, inquire about the patient's diet, including the following:

      • Amount of fish consumed

      • Frequency of consumption

      • Types of fish consumed

      • Source of fish consumed

      • Source of water supply

      Also inquire about classic symptoms, including the following:

      • Perioral and facial paresthesias

      • Extremity numbness

      • Dysarthria

      • Headache

      • Constriction of the visual fields

      • Difficulty in hearing

      • Memory loss

      • Problems with walking

      Methyl mercury exerts its most devastating effect on the CNS by causing the following:

      • Psychiatric disturbances

      • Ataxia

      • Visual loss

      • Hearing loss

      • Neuropathy

      Next:

      Physical Examination

      Although no physical findings are pathognomonic for mercury toxicity, the constellation of gait ataxia, tremulousness, hearing loss, visual field constriction, dysarthria, and distal limb sensory loss, coupled with cognitive and emotional dysfunction, is suggestive. Perform a complete neurologic examination, including a detailed cerebellar examination. Perform a full visual field evaluation. (Hearing loss and visual field impairments more often occur with organic poisoning, as in Minamata disease.)

      Perform abdominal and rectal examinations, with stool guaiac testing, and include documentation of a skin examination.

      Distal sensory loss, uncoordinated limb movements, resting tremors, gait ataxia, and a positive Romberg sign have been described after exposure to organic and inorganic mercury. A 2004-2005 study of 197 Minamata Bay residents who were exposed to methylmercury before 1968 found 90% with sensory impairments on the bedside neurologic examination. [64]

      Cranial neuropathies are very rare, but sixth and third nerve palsies were described in a man who injected himself with subcutaneous elemental mercury. [65]

      Emotional instability and cognitive impairments can be present in both types of exposure; however, these deficits are more characteristic of acute inorganic mercury toxicity. Neuropsychological testing in these cases has revealed pronounced impairments in traditional frontal lobe domains. [66]

      Low-level organic mercury exposures have been controversial. A study of 129 residents of fishing villages in Brazil reported that higher hair mercury levels were associated in a dose-dependent manner with reduced response inhibition and manual dexterity. [67]

      In addition, elevated blood mercury levels were associated with significantly reduced visual recall but improved manual dexterity in 474 elderly people in Baltimore, Md. Other tested domains were unaffected, and because of the disparate results, these researchers concluded that study provided no "compelling evidence" that blood mercury levels influenced the neurobehavioral status of their subjects. [68]

      In 240 adults living near an abandoned chlor-alkali factory in Taiwan, those with the higher blood methylmercury levels had significantly worse memory and mental manipulation abilities than did those with lower methylmercury levels. [69]

      Nonneurologic findings include skin changes, with contact dermatitis predominating, although cutaneous hyperpigmentation and stomatitis also occur. [70] Erythematous papules and papulovesicles, primarily on palms, have been reported to be associated with mercury toxicity attributed to seafood ingestion. [71] Respiratory distress can occur acutely in mercury poisoning.

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