Differential Diagnosis for a 2-year-old with Motor Weakness and Developmental Delay
- Single most likely diagnosis
- Duchenne's muscular dystrophy: This is a genetic disorder characterized by progressive muscle degeneration and weakness. It typically presents in early childhood, around the age of 2-5 years, with symptoms such as delayed walking, difficulty walking, and proximal muscle weakness. The fact that the child is having a hard time ambulating and is weaker than other siblings suggests a muscular dystrophy, with Duchenne's being the most common form in this age group.
- Other Likely diagnoses
- Cerebral palsy: While cerebral palsy is a condition that affects movement, muscle tone, and coordination, it is usually diagnosed earlier in life, and the symptoms can vary widely. However, it could be considered if the motor weakness is more pronounced in certain muscle groups and if there are other signs such as spasticity or dystonia.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Lead poisoning: Although less likely to present solely with motor weakness, lead poisoning can cause a range of neurological symptoms including developmental delay, and it is crucial to rule out due to its potential for severe and irreversible damage if left untreated.
- Rare diagnoses
- Other muscular dystrophies (e.g., Becker's muscular dystrophy, though less severe than Duchenne's), congenital myopathies, or metabolic myopathies could be considered but are less likely given the specific presentation and age of the child.
For the purpose of USMLE Step 3, recognizing Duchenne's muscular dystrophy as the single most likely diagnosis based on the age of presentation and the specific symptoms of motor weakness and delayed ambulation is key. However, it's also important to be aware of other potential diagnoses, especially those that could have serious consequences if missed, such as lead poisoning.