Reduced amplitude of the ulnar motor nerve and the sural nerve action potentials may be specific to transthyretin familial amyloid polyneuropathies (TTR-FAPs), allowing us to distinguish this disorder from other demyelinating polyneuropathies (ie, chronic inflammatory demyelinating polyneuropathy and polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes [POEMS]), according to a study published in Neurology.
This study consisted of a retrospective analysis of clinical and electrophysiologic features of 194 patients with FAP, 13 of whom were of French ancestry and had late-onset demyelinating FAP, as well as individuals with chronic inflammatory demyelinating polyneuropathy (n=21) and POEMS (n=19).
Features more frequently found in demyelinating familial amyloid polyneuropathies (dFAPs) compared with chronic inflammatory demyelinating polyneuropathy and POEMS included dysautonomia (risk ratio [RR] 7.8; 95% CI, 3.3-18.4), neuropathic pain (RR 9.3; 95% CI, 3.0-29.0), small fiber sensory loss above the wrists (RR 4.5; 95% CI, 2.23-39.1), absence of ataxia, and upper limb weakness (RR 4.0; 95% CI, 1.5-26.3). Asymmetric axonal loss was observed in 67% of peroneal nerves and in 63% of tibial nerves in dFAP. The most distinct characteristics of dFAP vs CDIP and POEMS included an action potential amplitude <3.95 μV for the sural nerve and a compound muscle action potential amplitude <5.4 mV for the ulnar motor nerve.
The retrospective design of the analysis and the small number of records examined are the study’s main limitations.
“[D]istinctive features of dFAPs [identified in this study] could be used as red flags by physicians to prompt [transthyretin] genetic testing, enabling earlier diagnosis of FAP and initiation of specific treatments, thus improving the clinical course of the neuropathy and patient survival,” concluded the investigators.
Lozeron P, Mariani LL, Dodet P, et al. Transthyretin amyloid polyneuropathies mimicking a demyelinating polyneuropathy. Neurology. 2018;91(2):e143-e152.