Peripheral nerve involvement in primary systemic AL amyloidosis: a clinical and electrophysiological study

Involvement of visceral organs usually dominates the clinical picture of primary systemic AL amyloidosis, but some patients suffer from serious peripheral neuropathy. The aim of this study is to clinically and electrophysiologically investigate peripheral nerve involvement in AL amyloidosis patients.

We reviewed clinical manifestations, electrophysiological findings including nerve conduction velocities and treatments in 43 consecutive patients. Twenty age-matched healthy subjects were employed as controls.

Fifteen patients (34.9%) showed apparent neuropathic symptoms, which consisted of polyneuropathy in 11 (25.6%), bilateral carpal tunnel syndrome in 4 (9.3%), and autonomic dysfunction in 8 (18.6%). Polyneuropathy in this disease was characterized by symmetrical and sensory-dominant impairment, early involvement of the lower limbs, loss of all sensations, rarity of motor weakness, and painful paresthesia in the legs predominant at an early stage. Autonomic dysfunction including orthostatic hypotension was frequently associated with polyneuropathy at an advanced stage. On electrophysiological studies, motor conduction velocity and compound muscle action potential of both median and tibial nerves were significantly decreased in the patients with polyneuropathy but also in those without any signs of neuropathy. Only four of 15 patients with neuropathy were able to receive intensive but promising chemotherapy with a large dose of melphalan for plasma cell dyscrasia.

Peripheral nerves in primary systemic AL amyloidosis patients seem to be involved more extensively than clinical manifestations might suggest. The clinical picture of polyneuropathy in this disease closely resembles that in transthyretin-type familial amyloid polyneuropathy patients with a late age at onset, particularly those originating from sporadic kindreds.