A four-year old boy is noted by teachers to be unable to keep up with his classmates in physical exercise. He tires easily and has difficulty climbing up stairs. He was slow to walk unaided (22 months) and has been prone to falling. He had speech development delay. There is no family history of note and he is otherwise well. On examination he has large, bulky calves but otherwise is well with no rash or nail fold capillary loop changes. He struggles to get up from the floor suggestive of proximal weakness. His Gower's test is positive - see pREMS Gait.
Examples of abnormal gait due to muscle disease are available.
What is the differential diagnosis?
The differential diagnosis includes causes of muscle weakness and must exclude muscular dystrophies, congenital myasthenic syndromes and inflammatory muscle disease. The absence of rash and nail fold capillary loop changes makes juvenile dermatomyositis unlikely. Polymyositis presents with muscle weakness without rash and nail fold capillary loop changes. Inherited myopathies are more likely with delay in development - inflammatory myopathies are more likely with regression of abilities.
Muscle enzymes - the creatine kinase levels are grossly elevated at 18,000 IU/L.
What is the likely diagnosis?
The diagnosis is muscular dystrophy (likely Duchenne Muscular Dystrophy). Refer to a muscle specialist is warranted.