Two-year follow-up of two patients after severe thallium intoxication.

Information on the prognosis and electrophysiological follow-up of severe thallium poisoning is limited. We report two patients (mother and daughter) who were repeatedly exposed to thallium poisoning experienced hair loss, polyneuropathy, and visual impairment. Nerve conduction studies (NCSs), visual evoked potentials (VEP), brainstem auditory evoked potentials (BAEP) changes, and optical neuropathy developed within a few months latency after the first subjective signs. Normal findings of these electrophysiological methods in the first 2 weeks therefore led in one of our patients to exclusion of thallium as the cause of symptoms. Thallium poisoning was, however, later confirmed by toxicological analysis of blood and/or urine and feces in both the patients and in the microscopic hair analysis of the daughter. Both patients were treated with Prussian blue that increased the elimination of thallium in urine and feces. The hair loss was fully reversible. During a 2-year follow-up after the poisoning, polyneuropathy in the lower extremities improved substantially, but residual impairment in both motor and sensory function, NCSs, VEP, and BAEP remained. Additionally, severe asymmetrical vision impairment persists in both women, with central scotomata and impaired color discrimination in both eyes. Substantial improvement of their visual function is unlikely.