Magnetic resonance imaging of lower limb musculature in acute motor axonal neuropathy.

Magnetic resonance imaging (MRI) is an extremely useful technique to diagnose muscle denervation. This report presents an acute motor axonal neuropathy (AMAN) patient in whom, over 2 years, serial clinical-electrophysiological evaluation and MRI examination of lower limb musculature were performed. A 74-year-old patient was admitted with a 24-h history of ascending weakness culminating a few days later in flaccid and areflexic tetraplegia, which was followed by progressive improvement except for severe residual paresis of foot flexors/extensors. Electrophysiological studies showed motor nerve conduction abnormalities characteristic of AMAN, and profuse signs of active denervation in foot and lower leg muscles, and to a much lesser degree in the thigh muscles. On MRI, T2- and T2-fat suppressed (T2FS) images showed an early (up to month 2 after onset) and subtle hypersignal of all four lower leg muscle compartments evolving to an extensive and widespread hypersignal (as of month 6). Progressive hypersignal of lower leg musculature on T1-weighted images, indicative of fatty atrophy, was detected as of the first year. Thigh and pelvic musculature exhibited early and reversible hypersignal on T2 and T2FS images. There was good concordance between clinico-electrophysiological and MRI findings. We conclude that serial MRI may be very useful to evaluate the extent of muscle denervation and to assess clinical course in AMAN.