MEDizzy - A 20-year-old man presents for evaluation of weakness of his

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Neuromuscular I

A 20-year-old man presents for evaluation of weakness of his face and upper extremities, gradually progressive over the past few years. The patient has a nearly expressionless face, with difficulty closing his eyes tightly and pursing his lips. He has asymmetric proximal upper extremity weakness with difficulty lifting his arms above his head. He also has weakness of foot dorsiflexion. On examination, there is muscle atrophy, more prominent proximally in the upper extremities, with evidence of winged scapula. Interestingly, his upper arms seem “thinner” than his forearms, but his deltoids are relatively spared. Creatine kinase is 510 IU/L (normal 220 IU/L). Which muscular dystrophy does he most likely have?

ExplanationThis patient has facioscapulohumeral muscular dystrophy (FSHD). This condition is inherited in an autosomal dominant fashion and is caused by deletions in a 3.3 kb repeating sequences, termed D4Z4, located on chromosome 4q35. FSHD is slowly progressive, and predominantly affects the face and shoulders, though later in the course of the disease, the lower extremities are affected as well. Age of onset is on average 16 in males and 20 in females, but can be variable, ranging between the first and sixth decades of life. These patients have weakness that can be asymmetric, and present with difficulty lifting their arms above their head, with prominent involvement of the upper arms (scapular muscles, biceps, triceps, trapezius, serratus anterior, and pectoralis), with relative sparing of the deltoids. The upper arm seems to be more atrophic than the forearms, making the bones of the shoulder appear prominent. Facial weakness is evident, with weakness of the orbicularis oculi, zygomaticus, and orbicularis oris. There is also weakness of the lower abdominal muscles, producing 832 the “Beevor sign,” in which the umbilicus moves upward with neck flexion. Pelvic muscles are compromised later. Weakness of foot dorsiflexion with preservation of plantar flexion strength is characteristic. The masseters, temporalis muscle, extraocular muscles, and pharyngeal and respiratory muscles are usually spared. Cardiac involvement is rare and intelligence is typically normal. Creatine kinase levels are normal to slightly elevated. The other options are unlikely in this case. Duchenne muscular dystrophy is discussed in questions 19 and 20. Becker’s muscular dystrophy is discussed in questions 30 and 31. Emery–Dreifuss muscular dystrophy is discussed in questions 51 and 52. Myotonic dystrophy is discussed in questions 7 and 12.