CASE NUMBER 544

Clinical History:  A 5-year-old boy is brought to the pediatrician because his parents notice that he walks on his toes and has difficulty climbing stairs. They state that he did not begin walking until he was 18 months old. Physical exam reveals bilaterally enlarged calves. A muscle biopsy is performed.

Image Gallery:

The low power view (left) shows fatty replacement of muscle fibers and hypertrophy and atrophy of fibers. The higher power view (right) shows marked fibrosis, fiber splitting, degeneration/myophagocytosis, and regeneration (internal nuclei).
Review Skeletal Muscle Histology
Norm No. 18 Skeletal muscle
[ImageScope] [WebScope]

Skeletal muscle fibers have striations which are easily seen on the longitudinal section. Nuclei are located at the periphery of normal striated muscle fibers.

Clinical History (continued): Immunohistochemical stains reveal complete absence of dystrophin protein and DNA sequencing confirms a deletion in the gene encoding this protein.

544-1b. Based on all of this information, what is the final diagnosis and why?

 

544-2. High serum levels of which of the following are frequently elevated in the early stages of this disease?

  1. Alkaline phosphatase
  2. Anti-Mi-2 antibodies
  3. Creatine kinase
  4. Mutation in the DMPK gene
  5. Thyroid hormone

 

544-3. Which of the following differentiates this patient’s disease from Becker muscular dystrophy (BMD)?

  1. BMD has some dystrophin expression
  2. BMD is more common in female patients
  3. BMD patients have a shorter lifespan
  4. BMD typically manifests earlier than this patient’s disease
  5. Cardiac involvement is not seen in BMD