A Case of Atypical Acute Encephalopathy Unmasking IgA Multiple Myeloma.

Multiple myeloma (MM) can have an insidious onset, particularly in its early stages, which may contribute to delays in diagnosis. Acute encephalopathy is a rare and atypical manifestation of MM that can further complicate timely recognition and management. We present the case of a 57-year-old woman who initially reported fatigue, back pain, recurrent falls, and significant unintentional weight loss and was found to have hypercalcemia, anemia, acute renal dysfunction, and bone lesions. Her clinical course rapidly evolved into profound encephalopathy, characterized by a change in mentation from her baseline, agitation, and eventual unresponsiveness requiring intubation. Extensive investigation, including a bone biopsy, revealed elevated IgA lambda paraproteins consistent with MM. She also had borderline serum hyperviscosity, mildly elevated ammonia levels, and diffuse microhemorrhages on brain MRI. Despite interventions, including plasmapheresis and high-dose steroids, her encephalopathy persisted until initiation of bortezomib-based chemotherapy, resulting in neurological improvement. This case emphasizes the importance of recognizing MM as a potential cause of unexplained encephalopathy and highlights the complexity of its neurological manifestations, underscoring the need for prompt hematologic evaluation and interdisciplinary management.