Differential Diagnosis for 6-year-old with Knee Pain and Rash
- Single most likely diagnosis:
- Henoch-Schönlein Purpura (HSP): Given the patient's history of a lacy erythematous rash on the extremities, sparing the trunk and face, and the recent trauma to the knee, HSP is a strong consideration. The rash's initial response to prednisolone and subsequent recurrence also supports this diagnosis. HSP is a common vasculitis in children that can present with joint pain, rash, and gastrointestinal symptoms.
- Other Likely diagnoses:
- Traumatic knee injury: The patient's recent trauma to the knee could be causing the pain, and the rash could be unrelated.
- Ehlers-Danlos syndrome-related complications: The patient's history of Ehlers-Danlos syndrome could contribute to joint instability or other musculoskeletal issues, potentially exacerbating the knee pain.
- Allergic reaction or contact dermatitis: The rash could be an allergic reaction or contact dermatitis, especially given the patient's history of playing in the park.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Septic arthritis: Although less likely, septic arthritis is a medical emergency that requires prompt diagnosis and treatment. The patient's knee pain and recent trauma could be indicative of a septic joint.
- Osteomyelitis: Similar to septic arthritis, osteomyelitis is a serious infection that requires prompt treatment. The patient's knee pain and recent trauma could be indicative of an underlying bone infection.
- Meningococcemia: Although rare, meningococcemia is a life-threatening condition that can present with a rash and joint pain. It is essential to consider this diagnosis, especially given the patient's rash and potential for rapid deterioration.
- Rare diagnoses:
- Juvenile idiopathic arthritis (JIA): Although less likely, JIA could be a consideration, especially given the patient's joint pain and rash.
- Vasculitis (other than HSP): Other forms of vasculitis, such as Kawasaki disease or polyarteritis nodosa, could be considered, although they are less likely given the patient's presentation.