Differential Diagnosis for a 6-year-old with Knee Pain and Rash
- Single most likely diagnosis:
- Henoch-Schönlein Purpura (HSP): This condition is characterized by a lacy, erythematous rash on the extremities, sparing the trunk and face, which matches the patient's presentation. The rash's recurrence after initial resolution with prednisolone is also consistent with HSP. Additionally, HSP often presents with joint pain, which could explain the patient's knee pain after a minor trauma.
- Other Likely diagnoses:
- Juvenile Idiopathic Arthritis (JIA): Although the rash is not typical for JIA, the joint pain and rash could be indicative of this condition. However, the rash's description and distribution are more suggestive of HSP.
- Allergic Contact Dermatitis: The rash could be an allergic reaction to something the patient came into contact with while playing in the park. However, the rash's appearance and the patient's joint pain make this diagnosis less likely.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Meningococcemia: Although the rash's appearance is not typical for meningococcemia, it is essential to consider this diagnosis due to its high mortality rate if left untreated. However, the patient's overall presentation and the rash's distribution make this diagnosis less likely.
- Lyme Disease: If the patient was exposed to ticks while playing in the park, Lyme disease could be a consideration. However, the rash's appearance and the patient's joint pain are not typical for Lyme disease.
- Rare diagnoses:
- Vasculitis (e.g., Polyarteritis Nodosa, Granulomatosis with Polyangiitis): These conditions are rare in children and would typically present with more systemic symptoms. However, they could be considered if the patient's symptoms worsen or do not respond to treatment for HSP.
- Rheumatic Fever: Although the patient's presentation is not typical for rheumatic fever, it could be considered if the patient has a history of streptococcal infection and develops additional symptoms such as carditis or chorea.