Clinical Case Study
Disorders of Bone, Muscle, Ligaments, and Tendons |
HPI: MK is a 4-year-old boy brought into your office by his mother, who is concerned about his strength and coordination. She reports that he was fine up until a few months ago, and since then he seems to be more clumsy and has difficulty getting up from a kneeling or sitting position and climbing the stairs. PMHx: His pregnancy, labour, and delivery was uncomplicated, and he has met all his milestones to date. P/E: MK is a well-appearing young boy in no distress. His vitals are stable. An extremity exam reveals proximal muscle weakness bilaterally and enlarged calf muscles. When asked to rise from a sitting position, he uses his arms to push up on his thighs, helping his body to rise (see Figure 1). He demonstrates a waddling gait. The remainder of his examination is normal. |
Figure 1 |
| Question | Your Answer |
What is the most likely diagnosis? |
Duchenne’s muscular dystrophy (DMD). |
What lab test would help confirm your suspicions? |
Creatine kinase is grossly elevated in cases of DMD. Confirmation comes from a muscle biopsy that reveals muscle fibre necrosis and is absent of dystrophin on staining. |
Is there a genetic component to this condition? |
DMD is a classic X-linked recessive condition. The dystrophin gene is one of the largest in the human genome. Family history is important, but it may be uninformative as some cases represent spontaneous mutations. |
Why are his calves enlarged? |
DMD is also called pseudohypertrophic muscular dystrophy as it creates muscles that appear enlarged but that ironically weaken progressively. The enlargement is not due to increased muscle but rather due to replacement of skeletal muscle cells by fat and fibrous connective tissue. |
What is the pathophysiology of this condition? |
The dystrophin gene codes for the dystrophin protein that helps link the intracellular matrix of skeletal muscle cells with the extracellular matrix. Mutations in the gene leading to DMD cause cell necrosis and death. |
What treatment options are there? |
While the gene and mutations have been identified, there is no cure, to date. This is a progressive disease with progressive muscle weakness leading to loss of ambulation in the early teens. Death in the late teens or early twenties is usually due to respiratory or cardiac failure. |