Shaking up the Salpetriere: Jean-Martin Charcot and mercury-induced tremor.

OBJECTIVE: To analyze Jean-Martin Charcot's studies of mercury-induced tremor.
METHODS: This study examines Charcot's original notes on mercury intoxication from the Bibliothèque Charcot, Paris, and his show-and-tell patient presentations that were hand-transcribed by his students and later published.
RESULTS: Using his standard method of presenting multiple patients with a similar disorder side by side, Charcot assembled a series of patients with mercurial intoxication from the clinics of Paris. He emphasized the rest and action components of mercury-induced tremor and stressed the value of using graphical tremor recordings rather than relying only on visual observation. He drew attention to the importance of air ventilation to avoid intoxication and of removal from intoxicating environments. He distinguished the characteristics of mercury-induced tremor from tremor associated with Parkinson disease, multiple sclerosis, and general paresis. Based on the similar intention tremor in multiple sclerosis and mercury intoxication, human pathology studies in multiple sclerosis, and animal experiments with mercury, he suggested that axonal demyelination underlay this form of tremor in both conditions, the former restricted to the CNS and the second to peripheral nerves.
CONCLUSIONS: These cases illuminate Charcot's diagnostic strategy and his reliance on the clinico-anatomic method to correlate pathology with clinical signs. Whereas much of Charcot's work emphasized hereditary etiologies of neurologic disease, these examples allow an understanding of his views on environmental factors in neurologic disorders as well as treatment strategies.