Thallium Toxicity: Complexities of Diagnosis and Management
Introduction: Thallium is a heavy metal, best known as a rodenticide that is occasionally involved in intentional or accidental poisonings. On average, one case of thallium toxicity is reported each year. Classically, thallium toxicity presents acutely with gastrointestinal symptoms, and chronically as peripheral neuropathy with alopecia. Many cases result in neurologic impairment or death, due to delay in diagnosis. Several treatment regimens have been proposed for thallium toxicity, but no single approach has been advantageous. We describe a case of thallium toxicity with rising in-hospital thallium levels treated with Prussian blue and Continuous Renal Replacement Therapy (CRRT). Case: A 41 year old man originally presented with abdominal pain and bilateral lower extremity paresthesia. He was diagnosed with atypical Guillan-Barré Syndrome, received four days of intravenous immunoglobulin and was discharged to neurorehabilitation. He presented 10 days later with personality changes, hallucinations, abdominal pain and worsening bilateral lower extremity paresthesia. His physical exam was significant for plantar sensory loss, 4/5 strength in bilateral lower extremities, absent patellar and Achilles reflexes and alopecia. Initial workup, including heavy metal screen was negative. Electromyography demonstrated a subacute distal axonal peripheral neuropathy. After an extensive workup, a serum thallium level drawn seven weeks after symptom onset was noted to be elevated at 158 ng/ml (reference 0-1ng/ml). The serum thallium level increased to 197 ng/ml prior to initiation of CRRT and Prussian blue therapy. The patient received a total of 30 days of Prussian blue and 22 days of CRRT with neurologic improvement. After extensive investigation, the source of the thallium was not found. Discussion: Although well defined, thallium toxicity is extremely rare and therefore difficult to diagnose. Thallium is not routinely included in heavy metal screening. Although the source of thallium was not found in this case, we suspect that thallium was being surreptitiously administered in the hospital. The acute rise in serum thallium cannot be explained by mechanisms that cause tissue redistribution. Finally, CRRT with administration of Prussian blue was successful in treatment of chronic thallium toxicity. Success of CRRT is most likely due to the fact that in this case, thallium was already distributed into the tissues and not concentrated in the circulation, as in acute thallium toxicity. This case poses a diagnostic challenge for the internist who will need to have a high index of suspicion for thallium toxicity, as a delay in treatment may be life threatening.