Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 9 3 2024 12 08 125 132 Morteza Daraei Department of Internal Medicine, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. Ahmad Khajeh-Mehrizi Department of Hematology and Medical Oncology, Cancer Institute, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. Behrooz Amirzargar Department of Otorhinolaryngology-Head and Neck Surgery, Otorhinolaryngology Research Center, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. Fereshteh Ameli Department of Pathology, Cancer Institute, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. Fahimeh Zeinalkhan Advanced Diagnostic and Interventional Radiology Research Center (ADIR), Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. 2024 10 18 2024 10 20 Sudden sensorineural hearing loss (SSNHL) as the initial manifestation of multiple myeloma (MM) is rare. We present a 45-year-old woman with hyperviscosity syndrome (serum viscosity of 10.2 cP) from MM who presented with hearing disturbance that responded dramatically to plasma exchange with saline and intratympanic steroid treatment. Serum protein electrophoresis confirmed the presence of a monoclonal band, and bone marrow biopsy showed a hypercellular marrow with 90% plasma cells, which demonstrated lambda monoclonal restriction. https://crcp.tums.ac.ir/index.php/crcp/article/view/993 https://crcp.tums.ac.ir/index.php/crcp/article/download/993/670