Mercury poisoning-associated membranous nephropathy and autoimmune encephalitis

Mercury intoxication is not uncommon and often presents with diverse symptoms of multiple systems. While neurological disorders and renal impairments have been examined in isolation, the concurrent occurrence of systemic symptoms linked to immune dysregulation is infrequently observed. Here, we report an unusual case that a 55-year-old male patient, who is a scrap merchant, was admitted to our center for neuropsychiatric disturbances, including incoherent speech and hallucinations. He was initially diagnosed with autoimmune encephalitis (AE) because of double positivity for CASPR2 and LGl1 antibodies in serum. The patient later presented with pruritus and nephrotic syndrome, where renal biopsy revealed membranous nephropathy (MN). In view of the mercury exposure history and elevated urinary mercury level, AE and MN were suspected to be related to mercury poisoning. The patient achieved a full recovery following a four-month treatment regimen comprising immunosuppressants and mercury-chelating agents, underscoring the significance of recognizing environmental toxins such as mercury in the coexisting diseases of different systems such as AE and MN.