Novel Isolated Cerebral AL&lgr; Amyloid Angiopathy With Widespread Subcortical Distribution and Leukoencephalopathy Due to Atypical Monoclonal Plasma Cell Proliferation, and Terminal Systemic Gammopathy

Neuropathologic and biochemical findings in a 34-year-old man whose disease began 2 years before death appearing as chronic progressive encephalitis and culminated in mutism are reported. Cerebrospinal fluid and serum of the patient showed a brain-restricted monoclonal &lgr;-light chain apparently produced by a small monoclonal immunoglobulin G&lgr; plasma cell population. In the preterminal stage, there was a systemic monoclonal gammopathy, the source of which could not be identified. At autopsy, there was extensive amyloid deposition in most vessels throughout the cerebral and cerebellar white matter, basal ganglia, and thalamus and diffuse leukoencephalopathy; cerebral and cerebellar cortices, other portions of the CNS, and non-CNS tissues were spared. Partial amino acid sequence analysis demonstrated that the amyloidogenic protein originated from immunoglobulin &lgr;-light chains which were produced by monoclonal plasma cells. There are 2 similar cases reported in the literature. The distribution of AL&lgr; deposits in these 3 cases indicates that widespread subcortical vascular amyloidosis with leukoencephalopathy is a novel clinicopathologic entity distinguished from other cerebral diseases with local amyloid light chain deposition, including amyloidoma, leptomeningeal vascular amyloidosis, solitary intracerebral plasmacytoma, primary intracerebral lymphoma with plasmacytic differentiation, and multiple sclerosis with demyelination-associated amyloid deposition.