Muscle Disease

Educational Gaps

1. Duchenne muscular dystrophy (DMD) may be mistaken for liver disease because of elevated serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Sometimes, especially in the early stage, when the child does not have obvious or progressive muscle weakness, the patient may occasionally be subjected to unnecessary liver biopsy or other gastrointestinal diagnostic procedures. When a preschool boy with delay in walking and difficulty in running, as well as elevated ALT and AST levels, is seen, serum creatine kinase (CK) and γ-glutamic transpeptidase (GGTP) are useful to perform. If elevated serum CK but normal GGTP levels are detected, muscle diseases are most likely.

2. In a boy younger than 5 years, if serum CK is at least 50 times normal, large calf muscles are present, and inherited pattern is consistent with X-linked recessive trait, DMD is the most likely diagnosis. Blood dystrophin gene mutation study will confirm the diagnosis of DMD if out-of-frame mutation is detected.

Objectives

After completing this article, readers should be able to:

1. Know the clinical features of DMD.

2. Know the natural history and late complications of the muscular dystrophies.

3. Know the differential diagnosis of weakness and an increased serum creatine kinase level.

4. Know the laboratory studies available to diagnose muscle disease of childhood.

5. Formulate a differential diagnosis for a patient who has an acquired muscle disorder.

Case Study

A 4-year-old boy is seen in his pediatrician’s office for evaluation of toe-walking and delayed independent walking at age 2 years. On physical examination, he has hypertrophy of both calf muscles and pushes on the floor and his thighs to get up from the floor. His serum creatine kinase (CK) level is 20,000 …