Scenario: A 3-year-old boy is brought to his pediatrician to be evaluated for difficulty walking and clumsiness. According to his parents, the patient began walking at the age of 18 months, but in the past year he has begun to fall more frequently and has difficulty getting up from the floor; often supporting himself with his hands along the length of his legs. Birth and developmental history until symptom onset are reportedly normal. There is no contributing family history.

On physical examination, the young boy has significant muscle weakness of his hip flexors, knee extensors, deltoids, and biceps muscles. His calves are large, and he walks on his toes during ambulation. Laboratory studies reveal an elevated serum creatine kinase (CK) level of greater than 900 international units per liter (IU/L).

Electromyography (EMG) of his muscles reveals a myopathy. Nerve conduction studies reveal relative normal nerve function.

Question: Which of the major types of muscular dystrophy does this patient most likely present with? What are the hallmark characteristics of this type of muscular dystrophy?

Potential answers:

A. Duchenne muscular dystrophy

B. Congenital myotonic muscular dystrophy

C. Limb-girdle muscular dystrophy

D. Becker muscular dystrophy

Answer with rationale: A. Duchenne muscular dystrophy

Duchenne muscular dystrophy typically presents with pseudohypertrophy of the calves and a swift progression of symptoms beginning around 3 to 5 years old.

Congenital myotonic muscular dystrophy presents at birth, with a slow progression of hypotonia, muscle weaknesses, and cognitive impairments.

Limb-girdle muscular dystrophy typically presents during the teenage years and through into adulthood, pressing slowly with muscle weaknesses mainly in the shoulder and pelvic regions.

Becker muscular dystrophy presents closer to 11 years old, with a slow progression of muscle weaknesses most commonly focused in the shoulders, trunk, and limbs.

^{For more information see Chapter 244 in The Color Atlas of Physical Therapy}