Acrodynia is a manifestation of chronic mercury poisoning or idiosyncrasy to mercury. This symptom complex includes dermatological and systemic manifestations of exposure to various forms of mercury. It is a Greek term that means 'painful extremities.' In literature, it is addressed by other names like tropho-dermatoneurose, erythema arthricum epidemicum, erythredema polyneuropathy, hydrargyria, and Feer syndrome, but 'pink's disease' is the most common alternate name. Presently, acrodynia is a rare disease, but sporadic cases are often reported.
Acrodynia is related more often to the elemental form of mercury (quicksilver) inorganic salts then the organic forms. The elemental form is found either in liquid or vapor form and is widely used in thermometers, blood cuffs, batteries, dental amalgams, fluorescent light bulbs, etc. The inhalational toxicity of quicksilver is more severe as compared to oral toxicity. The organic forms of mercury can exist as short-chain, alkyl-mercury compounds (methylmercury and ethylmercury) or long-chain, aryl-mercury compounds (methoxyethylmercury and phenylmercury). In particular, the toxicity of organic forms is related to the consumption of contaminated seafood.
There is no exact data regarding the present prevalence of acrodynia. The disease is mostly seen in infants and young children. Newborn babies and adults are less vulnerable. The condition was prevalent in the first half of the 20 century in Europe, America, and Australia. It was present in every one in 500 children exposed to the mercury present in the dental amalgams. The incidences were more common in infants and children less than two years, highest among the age group of nine-month-old. The earlier research resulted in the withdrawal of mercury-containing tooth powders from the market and hence the decreased morbidity and mortality. Between 1939 and 1948, the official death record from acrodynia was 585 in England, which dropped to 57 in 1957 and seven in 1955.
In the present, only rare cases of acrodynia with varied presentations are reported in the literature, most of which are related to accidental exposure to mercury in non-occupational settings. Mercury-containing preservatives (thiomersal), calomel containing diaper powders, plant fungicides, anthelmintics, mercury ointments, certain bactericidal agents, alternate, medicine drugs, folk medicines, and interior latex paints pose a hazard of causing mercury toxicity in domestic settings. Certain traditional ayurvedic medicines contain a significant amount of mercury and have caused cases of acrodynia.
Mercury, in its various forms, has an affinity for the ubiquitous sulfhydryl groups in the tissues by forming covalent bonds. The interaction of mercury with many intracellular moieties results in dysfunction of enzymes, membrane transportation, and structural proteins. Locally, mercury can produce corrosive actions due to its oxidizing and corrosive action. Mercury absorption can manifest in varied forms due to its vast systemic involvement. The involvement of the immune system in the form of delayed hypersensitivity has been proposed in the causation of acrodynia. There can be genetic variation in the idiosyncratic sensitivity of individuals due to the toxic effects of mercury.
The mechanism of acrodynia may also involve adrenocortical hyperfunction, sympathovasomotor dysfunction, and catecholamine dysfunction. The inactivation of catecholamine-0-methyl transferase can explain arterial hypertension associated with mercury, which in turn increases serum and urinary epinephrine, norepinephrine, and dopamine. The neural degeneration associated with mercury poisoning is responsible for the painful extremities, peripheral neuropathy, and associated neuropsychiatric symptoms, as seen in acrodynia.
The toxic effects of mercury depend on the form of mercury, age of the individual, route of exposure, biotransformation, accumulation in the target organs, and comorbidities. The vaporized form of elemental mercury is more readily absorbed as compared to the oral or intravenous route. The elemental mercury can be volatile at room temperatures, and the volatility increases with the rise in temperatures and aerosolization. The absorption of elemental is insignificant on oral ingestion. Still, conditions like abnormal gastrointestinal (GI) motility, fistulae, and perforation can lead to the entry of elemental mercury in the peritoneal space where it can be oxidized to inorganic forms. The inorganic salts and organic forms of mercury are mainly absorbed by the gastrointestinal tract after oral absorption. The absorption of the organic forms of mercury is more rapid as compared to the organic salts due to their lipophilic properties.
Distribution and Biotransformation
After absorption, mercury gets widely distributed in the various body tissues, mainly the kidneys, liver, kidney, and the central nervous system. The vaporized form of elemental mercury has a high affinity of accumulation in the nervous system due to its lipid affinity. The toxicity of elemental mercury eventually depends on its conversion to ionic mercury by catalase enzyme. The inorganic forms of mercury have an affinity for renal tissue, in particular the renal tubules. The penetration of the blood-brain barrier by the mercury ions is poor due to low lipid solubility. The organic forms of mercury can get accumulated in the various tissues and cross the blood-brain barrier and placenta. The ease of transformation across the placental barrier has been associated with the neurological degeneration in the fetus, as documented in the prenatally exposed infants showing manifestations of Minamata disease. The methyl forms significantly get accumulated in the RBCs and the hair.
The elemental and inorganic forms of mercury are primarily excreted by glomerular filtration and tubular secretion. Lungs, skin, and feces eliminate a small amount of elemental and inorganic forms of mercury. The biological half-life of both these forms is estimated at nearly 30 to 60 days. On the other hand, the organic forms of mercury undergo significant enterohepatic circulation with a biological half-life of about 70 days.
The initial history can be vague and mimic other conditions. The common presenting signs in an affected child are irritability, peevishness, poor appetite, unexplained drowsiness, weight loss, apathy, painful extremities, and increased sweating. The parents may complain of decreased playfulness owing to muscle atrophy and pain. The initial signs are followed by redness of toes, fingers, and tip of the nose. Photophobia, conjunctivitis, and keratitis are often coexistent.
Other important signs include pruritis, pyrexia of unknown origin, drooling of saliva, degeneration of nails and teeth, swollen gums intention tremors, alopecia, miliaria, generalized weakness, sleep disturbances, and secondary skin infections.
The skin of palms and soles may show vesicular eruption and subsequent desquamation. The palms and feet may be found swollen and shows dusky discoloration. A morbilliform, scarlatiniform, or rubeoliform exanthem can be seen along with hemorrhagic puncta. The repetitive scratching of hands may cause lichenification, excoriation, and ulcerating pyoderma. The cutaneous features have been described as ‘puffy, pink, painful, paresthetic, perspiring, and peeling hands’ by one author.
A cutaneous biopsy may show non-specific findings of chronic dermatitis along with hyperplastic sweat glands. The blood pressure is raised, and the child often has tachycardia. The atrophy of muscles of pelvic and pectoral girdle should be assessed. Occasionally, the patient can show a ‘Salaam posture,’ in which he sits with the head between the legs and rubs the hands together. The nerve biopsy can show myelin destruction, perinuclear chromatolysis in anterior horn cells. The involvement of other systems may be evidenced by bronchitis, dyspepsia, and upper respiratory infections.
A thorough clinical history, along with an evaluation of the possible exposures in the domestic surroundings and the workplace, is crucial before commencing the workout. The laboratory evaluation should include the demonstration of mercury levels in the blood, urine, and body tissues. The initial exercise should consist of radiological evaluation, toxicological screening of blood and urine, basic metabolic panel, liver function tests, and complete blood profile. Spot urine collections can be used for creatinine estimations, but the urine mercury concentrations should be estimated by a 24-hour urine sample.
Gas chromatography and thin layer chromatography techniques are useful to differentiate the organic and inorganic salts of mercury. A toxicology screening should be done to rule out other heavy metal poisonings. Estimations of the urinary levels of vanillylmandelic acid, homovanillic acid, and 17-ketosteroid should be done in patients with concurrent hypertension and endocrinological involvement. Electroneuromyography, cardiovascular evaluation neuropsychological tests should be employed if necessary.
While making inferences, it is essential to note that there is no established correlation between the symptomatology of mercury toxicity and its concentrations in the body fluids. Literature has mentioned the mercury assay of hair in chronic poisonings but is prone to misinterpretations.
Elimination of the source of exposure is the first crucial step in initiating the treatment. The initial therapy should aim to correct the fluid and electrolyte imbalances. All cases of inhalational toxicity of elemental mercury need monitoring of vital organs. Whole-bowel irrigation by polyethylene and gastric decontamination by activated charcoal can be rarely indicated but can be attempted.
Meso 2,3-dimercaptosuccinic acid (succimer, DMSA) is an FDA approved water-soluble analog of BAL (British anti-Lewisite) and forms the mainstay of treatment. WHO recommends succimer therapy to be initiated in children with urine mercury levels ≥ 50 μg/mL creatinine, even if the child is asymptomatic. DMSA can be given orally or intravenously. The dose for children is 350 mg/m^2 three times daily for the first five days, then 350 mg/m^2 twice daily for the next 14 days. Depending on the remission of symptoms, the dose can be repeated after two weeks. The CBC, renal and hepatic functions of the child should be monitored during treatment. BAL (dimercaprol ) and D-penicillamine have also been used in the past for the treatment of acrodynia. The use of BAL should be avoided to treat mercury toxicity since it may aggravate the accumulation of mercury in the nervous system. In case of unavailability of succimer, D-penicillamine can be used in the daily dosage of 20 to 30 mg/kg in 4 divided doses. D-penicillamine is not useful for organic mercury toxicity and can cause more severe side effects like nephrotoxicity.
Antihypertensive drugs like tolazoline, amlodipine, and labetalol can be used to treat coexistent hypertension. Hemodialysis should be reserved for the refractory cases of renal failure secondary to mercury toxicity. The role of peritoneal dialysis and plasma exchange has also been described. Peripheral pain should be treated with gabapentin and pregabalin. Local application of ointments containing lidocaine and ketamine can be prescribed. Skin conditions like secondary infections and pyoderma can warrant the use of antibiotics as per the results of culture sensitivity. The diet must be encouraged in patients with anorexia. An environmental survey is essential for patient management in mercury poisoning. It should aim towards the decontamination of the domestic and industrial surroundings in a scientifically prescribed manner.
Diagnosis of acrodynia can be a difficulty for the clinicians due to the nonspecific systematic manifestations of mercury toxicity and rarity of the disease in the present times. The dermatological findings can be confused with other skin conditions like postviral acral desquamation, Kawasaki disease, juvenile plantar dermatosis, erythromyalgia, etc. Contact exposure to mercury can itself result in other cutaneous conditions like acute generalized exanthematous pustulosis and Symmetric flexural exanthema.
The involvement of other systems like the nervous, gastrointestinal, cardiovascular, and respiratory systems can complicate the diagnosis of acrodynia. The common systemic diseases confused with the diagnosis of acrodynia are pheochromocytoma, idiopathic hypertension in the pediatric age group, and Kawasaki disease. Simultaneously, toxicities of other heavy metals like gold, arsenic, copper, and thallium can mimic the clinical presentation of acrodynia. In the pediatric population, acrodynia can be misdiagnosed as brucellosis, hyperthyroidism, Guillain Barré syndrome, sepsis, etc. In the past, the clinical presentation of pink’s disease has been confused with viral infections and nutritional deficiencies.
The prognosis depends on the age, idiosyncrasy, the dose, and the duration of exposure. The prognosis can be variable but is often favorable. In the vast majority of cases, the symptoms get alleviated with chelation therapy. Elder children seem to have a better recovery. In earlier times, the fatality of deaths was as high as 10 to 33%. Infertility (Young disease), bronchiectasis, mental retardation, and permanent neurological deficits have been reported in the survivors. A high prevalence of autism spectrum disorders among descendants of survivors of pink’s disease is also documented.
Unfortunately, despite treatment, some patients are disabled and have a poor quality of life. The organic damage suffered from mercury is often irreversible and patients. The patients often have marked changes in intelligence and cognition. Patients with a short exposure to mercury can recover fully if mercury exposure is discontinued.
The diagnosis and management of acrodynia involve a high suspicion based on exposure and a multidisciplinary approach. Although various jurisdictions have imposed policies to curtain the exposure of mercury, the practitioners can encounter cases of acrodynia. There is a growing trend of intake of herbal and ayurvedic medicines, which may contain an abnormally high amount of mercury and its variants. The diagnosis of acrodynia can be challenging, given various conditions mimicking the clinical presentation. The health care professional should emphasize on an environmental survey, regular follow-up, and proper choice of the chelating agents for better treatment outputs.
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