Dropped head syndrome in anti-MuSK antibody-positive myasthenia gravis with possible concurrent axial myopathy

Abstract

Background

Dropped head syndrome (DHS) is a group of disorders that result in anterior neck flexion. Myasthenia gravis (MG) is a common cause of DHS. Previous reports have suggested that concurrent myopathy involving the paraspinal musculature may underlie DHS in patients with anti-acetylcholine receptor antibody-positive or thymoma-associated MG.

Case Presentation

A 64-year-old woman presented with a 3-month history of head drop and lordosis. Neurological examination revealed bilateral ptosis and weakness of the posterior neck extensors. Electrophysiology suggested neuromuscular junction involvement. Serum anti-MuSK antibodies were positive, and generalized anti-MuSK antibody-positive myasthenia gravis (MuSK-MG) was diagnosed. Needle electromyography (nEMG) of the splenius capitus and paraspinal muscles revealed acute and chronic myogenic changes. Imaging suggested paraspinal muscle atrophy. nEMG and magnetic resonance imaging (MRI) of both extremities were normal, and autoimmune myopathy-related antibody testing was negative.

Conclusion

Thymoma-negative MuSK-MG, demonstrating treatment-refractory DHS, may present with concurrent axial myopathy.