P-MU004. A rare treatable cause of dropped head syndrome

Abstract

Introduction . Dropped head syndrome results from neck extensor weakness, and is commonly due to neuromuscular disorders such as inflammatory myopathies, myasthenia gravis, or amyotrophic lateral sclerosis. We describe, with neck muscle imaging findings, a man presenting with neck extensor weakness due to hypothyroidism that resolves with thyroxine replacement. Results . A 60-year-old man without any past medical history of note presented with neck pain for 7 years. On examination, he was noted to have head drop, without limb weakness, bulbar symptoms nor fatiguability. Neurologic examination was otherwise normal. Creatine kinase (CK) was raised at 2480 U/L. Thyroid-stimulating hormone (TSH) was high at 64.50 mIU/L (Normal 0.45-4.50 mIU/L), and T4 was low at < 3.2 pmol/L (Normal 8-16 pmol/L). Thyroid peroxidase and anti-thyroglobulin antibodies were positive. Antiacetylcholine receptor and myositis-specific antibodies were negative. Repetitive nerve stimulation was negative. Needle electromyography showed evidence of an irritable myopathy in the deltoid, iliopsoas and neck extensors. Computed Tomography of the neck showed hypertrophy of the splenius capitis. He was diagnosed with myopathy due to hypothyroidism and started on levothyroxine replacement. 6 months’ later, there was resolution of his dropped head with normalization of his CK levels. Conclusion . Hypothyroidism more commonly presents with proximal limb weakness or raised CK. Associated axial myopathies are very rarely described. Hypothyroidism is a treatable cause of dropped head syndrome that reverses with thyroxine replacement. It is a rare cause of neck extensor muscle hypertrophy and irritable myopathy. Recognizing this entity is important to avoid unnecessary invasive investigations, such as muscle biopsy, or unnecessary immunomodulatory treatment in a neck extensor myopathy that will self-resolve with normalization of thyroid function. Muscle imaging can be helpful in its diagnosis.