Features of the DHS:
(1) There is a marked muscle weakness in the neck extensor muscles.
(2) The patient's chin rests on the chest while sitting or standing.
(3) The head position can be corrected by passive neck extension (not fixed).
Differential diagnosis of DHS:
(1) isolated neck extensor myopathy (INEM)
(2) amyotrophic lateral sclerosis (ALS)
(3) post-polio syndrome (PPS)
(4) chronic inflammatory polyneuropathy
(5) myasthenia gravis (MG)
(6) paraneoplastic myopathy
(7) Parkinson's disease
(8) polymyositis
(9) inclusion body myositis
(10) nemaline myopathy
(11) mitochondrial myopathy
(12) carnitine deficiency
(13) fascioscapulohumeral dystrophy
(14) myotonic dystrophy
(15) other congenital myopathy
(16) severe hypokalemic myopathy
(17) hypothyroid myopathy
(18) Cushing syndrome
