WHAT IS THE EXTENT AND NATURE, CLINICALLY AND ELECTROPHYSIOLOGICALLY, of peripheral nerve involvement in primary systemic AL amyloidosis? To address these questions, a retrospective review was undertaken of 43 such patients, previously untreated, admitted between April 2002 and June 2008 to the Department of Medicine, Shinshu University School of Medicine, Matsumoto, Japan. Diagnosis was based on tissue biopsy confirmation of amyloid deposition using Congo red and immunohistochemical staining. Records reviewed included the neurological examination, electrodiagnostic studies, past medical history, and blood and urine studies. Statistical analysis was provided by Student's t-test and Mann--Whitney's U test with P < 0.05 considered statistically significant. Neuropathic involvement, either mononeuropathy, polyneuropathy, or autonomic neuropathy, was evident in 15 patients (34.9%), including nine men and six women, with a mean age of 57.9 years and a mean disease duration of 14.7 months. Polyneuropathy was diagnosed in 11; in two of these it was the presenting symptom. Bilateral carpal tunnel syndrome was present in four, including one with polyneuropathy. Autonomic symptoms, encompassing orthostatic hypotension, hypohydrosis, impotence, urinary incontinence, and alternating diarrhea and constipation, were present in eight, only one of whom had neither polyneuropathy nor carpal tunnel syndrome. In all, sensory symptoms were predominant, with muscle weakness in the distal legs present in only three elderly patients. None had cranial nerve involvement. Electrodiagnostically, the polyneuropathy was predominantly axonal in nature, with decreased motor and sensory amplitudes but only minimal prolongation of terminal motor latencies and mild slowing of motor and sensory nerve conduction velocities compared to normal controls. Neuropathy is common in primary systemic AL amyloidosis and resembles that seen with the late-age-onset transthyretintype of familial amyloid polyneuropathy. [ABSTRACT FROM AUTHOR]