Differential Diagnosis for a 4-year-old with Subjective Weakness in Lower Legs
Single most likely diagnosis
- Benign Acute Childhood Myositis: This condition is characterized by acute onset of lower limb weakness, typically following a viral infection. The child's recent recovery from a cold infection and the presence of pain in the lower legs bilaterally support this diagnosis. The fact that the child has normal power and sensory sensations when lying down but is unable to stand suggests a condition that affects muscle strength in a position-dependent manner, which is consistent with benign acute childhood myositis.
Other Likely diagnoses
- Viral Myositis: Similar to benign acute childhood myositis, viral myositis can cause muscle pain and weakness, especially after a viral infection. However, it may not be as transient or benign.
- Growing Pains: Although typically not associated with significant weakness, growing pains can cause leg pain in children, especially at night or after activity. The child's complaint of pain could be related to growing pains, but the weakness is less characteristic.
- Muscle Strain or Overuse: If the child has been unusually active, muscle strain could lead to pain and weakness, especially if the child is not used to such levels of activity.
Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Guillain-Barré Syndrome: An autoimmune disorder that can cause rapid-onset muscle weakness, often following an infection. It's crucial to monitor for ascending paralysis and respiratory muscle involvement.
- Spinal Cord Lesions or Tumors: Although less likely, any spinal cord pathology could cause lower limb weakness. The absence of sensory deficits and normal deep tendon reflexes makes this less likely, but it cannot be entirely ruled out without further investigation.
- Neuromuscular Junction Disorders (e.g., Myasthenia Gravis): These conditions can cause fluctuating muscle weakness, which might worsen with activity. However, they are rare in children and typically present with more widespread or specific patterns of weakness.
Rare diagnoses
- Dermatomyositis or Polymyositis: Inflammatory myopathies that can cause muscle weakness and pain. They are rare in children and would typically be associated with other systemic symptoms or skin findings.
- Metabolic Myopathies: Disorders such as McArdle's disease can cause muscle pain and weakness after activity due to defects in muscle energy metabolism. These conditions are rare and might not present with the exact pattern described but should be considered in the differential diagnosis of recurrent or unexplained muscle weakness.