case report
Parkinsonism and irritability looked like primary psychiatry. Mercury poisoning did not.
2026-06-23
Parkinsonism and irritability looked like primary psychiatry. Mercury poisoning did not.
A decade of decline
A 60-year-old man presented to a neurologist with a 10-month history of worsening hand tremors, particularly in his right fingers, and difficulties with fine motor tasks. He was also suffering from insomnia, fatigue, and muscle cramps at rest.
What appeared to be a physical decline was accompanied by significant psychological changes. He was experiencing persistent irritability and emotional lability, which psychological testing later confirmed as an emotionally irritable profile with deficits in working memory and cognitive decline.
The standard labs return normal
Initial extensive medical workups failed to explain his symptoms. His complete blood count, kidney and liver function tests, thyroid panel, electrolytes, and viral serology for HIV and hepatitis were all within normal limits. Crucially, his serum Vitamin B12 and folate levels were also reported as normal.
Because the patient worked at a waste disposal center with frequent exposure to electrical devices, light bulbs, and varnished packaging, his physicians ordered a toxicological screening. The results revealed he was not just exhausted; his blood mercury was 15.2 μg/L, more than triple the reference limit of 5 μg/L. His hair mercury was also three times the normal level.
The body begins to fail
Despite the initial findings, the man's condition continued to deteriorate. He developed a spastic and rigid gait, slurred speech (dysarthria), and a loss of proprioception—the sense of where his limbs were in space. He felt constant tingling and numbness (paresthesia) in his legs and feet.
Doctors suspected Parkinsonism and trialed him twice on levodopa/benserazide and levodopa/carbidopa. The symptoms did not respond. A SPECT scan of his brain showed no dopaminergic loss, meaning the Parkinson’s drugs had nothing to treat. Meanwhile, an FDG-PET scan revealed hypometabolism in the temporal and parietal regions of his brain.
The hidden deficiency
While his serum B12 levels had looked normal, a more specific test revealed a functional deficiency. His methylmalonic acid was elevated, signaling that while B12 was present in his blood, it was not being utilized correctly by his cells. Mercury is known to inhibit enzymes like methionine synthase, effectively "locking" the body's ability to use B12.
MRI imaging of the cervical spine finally showed the physical consequence: morphological changes in the posterior cord from C3 to C7. This was subacute combined degeneration, a classic result of B12 deficiency, now linked to his chronic mercury exposure.
Recovery through detoxification
Treatment shifted from psychiatric and Parkinson’s medications to detoxification. He was started on N-acetylcysteine (4200 mg/day) to help his kidneys excrete the mercury, alongside selenium and high doses of vitamins B12, D, and E.
Over several years, his condition stabilized. While he remains moderately neurologically impaired with some tremors and weakness, his irritability has lifted and his general health has improved. He credits the diagnosis with saving him from further decline, noting, "We should all react promptly if there is a suspicion of the potential negative effects of toxic substances in our environment."
The medical picture
Blood Mercury
15.2 μg/L (Ref: <5)
Hair Root Mercury
3 μg/g (Ref: <1)
Urinary Arsenic
588.31 μg/L (Ref: <25)
Methylmalonic Acid
Elevated (marker of functional B12 deficiency)
CSF Protein (Proteinorachia)
704 mg/L (Ref: 170–370)
Adapted faithfully from the open-access case report: Frontiers in Toxicology (PMC12454407). DOI: 10.3389/ftox.2025.1580275. Read the original at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12454407/.