S41 What are the electrophysiological pitfalls in FAP?

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Introduction Familial amyloid polyneuropathy (FAP) is an autosomal dominant disease characterized by endoneurial amyloid deposits. Transthyretin FAP (TTR-FAP) is the most common type. The major clinic presentation of TTR-FAP is a progressive length dependent axonal sensorimotor and autonomic neuropathy. Methods Electrophysiological studies used in the diagnosis and follow-up are viewed. Results A standard electromyography (EMG) study consists of sensory and motor nerve conduction studies as well as late responses when assessing FAP. EMG studies are important in many aspects in the evaluation for FAP. In asymptomatic patients, neurological screening at periodic follow-up includes EMG. Early signs of peripheral nerve involvement like reduced sensorial nerve action potentials predominantly in lower extremities or typical manifestations like carpal tunnel syndrome can lead to decide the initiation of disease-modifying treatments. As the disease progresses, EMG studies commonly reveal symmetric motor and sensorial axonal degeneration. Asymmetric involvement is a rare clinical presentation. Some mild demyelinating signs like prolonged distal latencies of motor responses, mild reduced conduction velocities and prolonged latencies of late responses may be seen due to loss of fast conducting fibers in early stages. Atypical electrophysiological findings were also reported including fasciculations, findings of bulbar involvement, chronic inflammatory demyelinating polyneuropathy and pure motor neuropathy, in patients with relevant atypical presentations. EMG is also used in follow-up of treatment. Recently, sum scores with clinical and electrophysiological findings were recommended. Discussion EMG studies provide useful information for the diagnosis and follow-up of FAP. It is important to be aware of atypical presentations.