Primary cerebral immunoglobulin light chain amyloidoma in a patient with multiple sclerosis

A man in his 60s, known with multiple sclerosis, presented with seizures and paresis of the left arm and leg. Brain imaging showed a white matter lesion, right parietal, which was progressive over the last 6 years and not typical for multiple sclerosis. Brain biopsy showed a B-cell infiltrate with IgA lambda monotypic plasma cell differentiation and amyloid deposits, typed as lambda immunoglobulin light chain (AL). Bone marrow biopsy and PET/CT ruled out a systemic lymphoma. Extended history taking, blood and urine testing (including cardiac biomarkers) identified no evidence of systemic amyloidosis-induced organ dysfunction.Primary cerebral AL amyloidoma is a very rare entity where optimal treatment is difficult to assess. The patient was treated with locally applied volumetric modulated arc radiotherapy, 24 Gy, divided in 12 fractions. Afterwards, the paresis of the left arm partially resolved, and the function of the left leg improved. Seizures did not occur anymore.