Selective atrophy of the brachialis muscle in neuralgic amyotrophy: ultrasound imaging of fascicular nerve damage.

The most common presentation of neuralgic amyotrophy (NA), also known as brachial plexus neuritis or Parsonage-Turner syndrome, is acute unbearable pain more severe at night involving the shoulder, upper arm and cervical region followed by patchy weakness in the C5-C6 innervated muscles and less prominent sensory symptoms.1 NA presentations may range from single nerve to widespread brachial and lumbosacral plexuses involvement, and include painless, bilateral and pure sensory phenotype.1 NA pathophysiology includes genetic predisposition, autoimmune triggers and mechanical vulnerability, but the mechanisms are not understood and the recovery may be incomplete.1 We report imaging findings in two cases of NA with selective brachialis muscle (BM) atrophy and fascicular involvement of the musculocutaneous nerve (MCN). Case 1 : A 46-year-old right-handed woman reported acute severe right upper limb pain after carrying a heavy load, followed by anterior arm muscles atrophy. Examination 4 months later showed BM atrophy (figure 1A) and elbow flexors weakness. Electrodiagnosis showed marked BM denervation. Nerve high-resolution ultrasound (HRUS) showed an enlarged MCN fascicle with thickened epineurium (figure 1B–C). MRI showed right BM degeneration (figure 1D–F). At 8-month follow-up there were no clinical/electrodiagnostic signs of reinnervation, while the recovery was nearly complete 4 years later. …