A 16-year-old boy presents with recurrent episodes of wrist drop and peroneal palsy after minor trauma or prolonged sitting. Nerve biopsy is characterized by sausage-shaped bulges of the myelin sheath. Considering the most likely diagnosis, a genetic test would most likely reveal which abnormality?
A 4-year-old boy presents with difficulty climbing stairs and frequent falls. Examination reveals enlarged calf muscles and a waddling gait. He uses his hands to push off his thighs to stand up. Which laboratory finding is most characteristic of this child’s condition?
A 17-year-old male presents with difficulty running and climbing stairs. On examination, he has weakness of his hip girdle muscles, but also notable weakness and atrophy of his calf muscles. His serum creatine kinase is chronically elevated in the thousands. A primary defect in which protein is associated with this presentation?
During the evaluation of a 6-year-old boy with progressive weakness, the neurologist notes that the weakness is predominantly distal, and tendon stretch reflexes are absent. In general, which component of the motor unit is most likely affected based on this distribution?
An adolescent with familial hypercholesterolemia was started on a statin medication. He now presents with severe, progressive muscle weakness and markedly elevated creatine kinase levels. An investigation reveals the presence of anti-HMG-CoA reductase antibodies. What is the most appropriate next step in management?
An 8-year-old boy with a known diagnosis of myotonic dystrophy type 1 is being evaluated. His mother notes he has trouble releasing his grip after making a fist. The physician taps the boy’s thenar eminence with a percussion hammer, observing an involuntary drawing of the thumb across the palm. What is the clinical term for this phenomenon?
An infant boy is diagnosed with severe, X-linked myotubular myopathy due to a pathogenic variant in the MTM1 gene. His mother is clinically asymptomatic. What would a muscle biopsy of the asymptomatic carrier mother most likely show?
An infant being evaluated for developmental delay is pulled from a supine to a sitting position. The infant’s head lags significantly behind the body. What does this specific physical exam finding primarily indicate?
A 13-year-old boy presents with clumsiness, frequent tripping, and difficulty running. Examination reveals bilateral foot drop, pes cavus, and wasting of the anterior compartment muscles of his lower legs. Nerve conduction studies show markedly reduced velocities. What is the most common underlying genetic defect for this condition?
An 11-year-old boy presents with calf pseudohypertrophy and complains of muscle cramps specifically during exercise. His weakness is mild, and he remains fully ambulatory. Which clinical presentation is most consistent with Becker muscular dystrophy as opposed to Duchenne muscular dystrophy?
