To report a case of parkinsonism following B-cell maturation antigen (BCMA)–directed chimeric antigen receptor T-cell (CAR T-cell) therapy, associated with abnormal dopamine transporter single-photon emission computed tomography (DAT-SPECT) findings.

Parkinsonism has been reported as a rare immune-mediated neurodopaminergic injury following BCMA-directed CAR T-cell therapy. DAT-SPECT is usually normal.

A 70-year-old African American man was first seen in 2011 with poorly controlled diabetes, monoclonal gammopathy of undetermined significance (MGUS), and painful neuropathy. His neuropathy, present for over 10 years and initially attributed to diabetes, was confirmed by EMG/NCS as an axonal sensorimotor polyneuropathy with mild autonomic and cognitive symptoms. MGUS remained stable for nearly a decade before progression to stage III multiple myeloma (MM) at age 65. He was treated with chemotherapy, immunotherapy, and autologous stem cell transplantation. Due to disease progression, he received BCMA-directed CAR T-cell therapy with ciltacabtagene autoleucel at age 68. Shortly thereafter, he developed cytokine release syndrome (CRS) and immune effector cell–associated neurotoxicity syndrome (ICANS), which improved with anakinra and dexamethasone. Five months post-therapy, he developed bilateral tremor, shuffling gait, and reduced left arm swing. Brain MRI showed mild white matter hyperintensities without basal ganglia involvement. DAT-SPECT demonstrated symmetric decreased radiotracer uptake in the striata, markedly reduced in the bilateral putamen, and moderately decreased in the bilateral caudate nuclei. Treatment with carbidopa/levodopa produced mild improvement. MM remained in remission following CAR T-cell therapy.

Poorly DOPA-responsive parkinsonism following BCMA-directed CAR T-cell therapy represents a rare but clinically significant delayed neurotoxicity. The symmetric rather than asymmetric DAT-SPECT abnormality, with bilateral caudate involvement early in the clinical course and temporal association with prior immune effector cell toxicity, suggests immune-mediated dopaminergic dysfunction rather than idiopathic Parkinson’s disease. Recognition of this potential complication is important for timely diagnosis and management.