Differential Diagnosis for a 5-year-old with Elevated CPK, Proximal Muscle Weakness, Hyporeflexia, and Normal NCS and Normal MRI Spine
- Single most likely diagnosis:
- Duchenne Muscular Dystrophy (DMD): This is a genetic disorder characterized by progressive muscle degeneration and weakness. The elevated CPK levels and proximal muscle weakness are consistent with DMD. Although the diagnosis typically presents earlier, the age of 5 is within the range for diagnosis, and normal NCS and MRI spine do not rule out DMD, as the disease primarily affects muscle tissue.
- Other Likely diagnoses:
- Becker Muscular Dystrophy: Similar to DMD but generally milder and with a later onset. The clinical presentation can be similar, with elevated CPK and muscle weakness.
- Limb-Girdle Muscular Dystrophy: A group of disorders that affect voluntary muscles around the shoulders and hips. Elevated CPK and proximal weakness are common, and the age of onset can vary.
- Congenital Muscular Dystrophy: Although typically diagnosed at birth or early infancy, some forms may present later with progressive muscle weakness and elevated CPK.
- Do Not Miss diagnoses:
- Metabolic Myopathies (e.g., McArdle disease, debranching enzyme deficiency): These conditions can present with muscle weakness and elevated CPK. While less common, missing these diagnoses could lead to inappropriate management and significant morbidity.
- Inflammatory Myopathies (e.g., Juvenile Dermatomyositis): Although the normal MRI spine and NCS might be less typical, these conditions can cause significant muscle weakness and elevated CPK. Early diagnosis and treatment are crucial to prevent long-term damage.
- Rare diagnoses:
- Mitochondrial Myopathies: A group of disorders affecting the mitochondria, leading to muscle weakness among other symptoms. Elevated CPK can be seen, but these conditions are rare and often involve other systems.
- Pompe Disease: A lysosomal storage disorder that can cause muscle weakness and elevated CPK. It's rare and typically presents in infancy, but late-onset forms can occur.
- Glycogen Storage Diseases: Certain types can cause muscle weakness and elevated CPK, though they are less common and might have additional symptoms related to glycogen metabolism.