In May, 2008, a 59-year-old accounts offi cer, who worked for a shipping line called MOL, sat down and missed his chair, landing on the fl oor. He did not seem seriously injured, but developed low back pain, so was taken to our emergency department. Examining doctors found no evidence of physical injury; radiography of the lumbar spine showed no abnormality. However, the patient constantly spoke of his lower back pain. He believed himself to be in his offi ce, and could not recall his name. Blood tests and electrocardiography gave normal results; the patient was not taking any prescribed or illicit drugs, and had no medical history of note. He was transferred to our psychiatric ward. After transfer, he knew he was in hospital, but could not remember why he had come. He insisted that MOL stood for Ministry of Labour (Singapore has no Ministry of Labour). He scored 22/30 on the mini mental-state examination (MMSE): short-term recall, calculation, orientation, and construction were impaired (the MMSE does not test long-term memory). He was well kempt, without evident hallucinations or delusions, but expressed an ambition to become prime minister. His aff ect was not grandiose, but blunted. His speech was slow and laconic. We noted that he shuffl ed, stooped, and was bradykinetic. Serological testing for syphilis and HIV, and concentrations of caeruloplasmin, vitamin B12, folate, ammonia, lactate, complement (C3, C4), and antibodies to the nucleus and to double-stranded DNA were all normal, as was the urinary concentration of mercury. Analysis of cerebrospinal fl uid, electro encephalography, and MRI of the brain showed no abnormality. The patient’s sister remarked that, for 2 weeks before admission, he had been under stress, because of a substantial increase in workload; however, she had not been aware of any unusual behaviour. The patient was reviewed by a medical and a psychiatric consultant, who diagnosed dissociative amnesia. 1 month later, his memory remained impaired. He could recall his English, but not his Chinese name. He could recall the name of the district where he lived, but not the rest of his address. His family celebrated his birthday on the ward; subsequently, he could recall the celebration, but not his date of birth. He occasionally asked about the outcome of a job interview, which he had not attended. His family remarked that he was more passive and shy than usual. 6 weeks after admission, psychometric investigation revealed impairments in nonverbal reasoning ability, processing speed, calculation, delayed recall of visual information, and attention to auditory information. Simultaneously, we received results of blood testing for mercury: the mercury con centration was 28 μg/L (normal <15 μg/L). We therefore prescribed penicillamine. Where had the mercury come from? The patient did not have amalgam dental fi llings, and had not received vaccines containing thiomersal; he had no occupational exposure to mercury. To our knowledge, therefore, the only possible source was diet—but the patient was unable to remember what he had eaten. The patient lived alone; however, his cousin reported that the patient ate tuna every day, and bought Chinese herbal tea from unlicensed traditional practi tioners. With penicillamine treatment, the blood mercury concentration decreased, and cognition gradually improved. We discharged the patient in July, 2008. He still had some anterograde and retrograde memory impairment; his blood mercury concentration was now 19 μg/L. When the patient was last seen, in October, 2008, psychometric testing showed global improvement. He was sacked while in hospital, and has not resumed work. He no longer takes herbal medicine or eats tuna. Mercury is found in fi sh (fi gure), especially large marine predators such as shark, tuna, and swordfi sh; some Chinese medicines contain mercury, notably in cinnabar or calomel. Features of mercury poisoning include gingivitis, intention tremor, and psychiatric symptoms such as excitability, irritation, insomnia, memory loss, and shyness. Validated neuropsychological tests can be of use in assessment. The blood concentration of mercury provides an estimate of extent of exposure; a longitudinal record of mercury poisoning can be obtained by analysis of scalp hair.
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Oct 1, 2011
Doron Rimar + 4
Open Access
