Dropped head syndrome leading to the diagnosis of antisynthetase syndrome: a motor neuron mimicker.

BACKGROUND

Antisynthetase syndrome (ASS) is a rare subtype of idiopathic inflammatory myopathies that may present with muscular and/or extra-muscular features, sometimes delaying diagnosis. Dropped head syndrome (DHS) is an uncommon manifestation of axial muscle weakness and can mimic motor neuron disease or myasthenia gravis.

CASE PRESENTATION: We report the case of a 64-year-old male presented with dropped head and proximal weakness. Initial electromyography (EMG) revealed fibrillation potentials, positive sharp waves during rest, and signs of reinnervation during voluntary contraction, initially raising concern for a neurogenic process. Because of increased jitter on single-fiber EMG, myasthenia gravis was considered, but pyridostigmine provided no benefit. Although creatine kinase (CK) was only mildly elevated, myositis-specific autoantibodies, inflammatory biopsy changes, and myopathic features on repeat EMG, especially in cervical paraspinals, led to a diagnosis of ASS. Chest Computed Tomography (CT) revealed bibasilar bronchiectasis and micronodules.

CONCLUSION

This case highlights the diagnostic challenge of distinguishing ASS from motor neuron disease or myasthenia gravis. Inflammatory myopathies should be considered in DHS, with careful selection of muscles and interpretation of EMG findings, especially when CK elevation is modest.