Differential Diagnosis
- Single most likely diagnosis
- Henoch-Schönlein Purpura (HSP): This condition is characterized by the presence of palpable purpura, joint pain (especially in the ankles), and scrotal swelling, all of which are present in this patient. The symmetrical distribution of lesions and the absence of fever, headache, or diarrhea also support this diagnosis.
- Other Likely diagnoses
- Infectious endocarditis: Although less likely given the absence of fever and heart murmurs, the presence of palpable purpura and joint pain could suggest an infectious etiology. However, the lack of other typical symptoms makes this less probable.
- Vasculitis (e.g., microscopic polyangiitis, granulomatosis with polyangiitis): These conditions can present with similar symptoms, including palpable purpura and joint pain. However, they often have additional symptoms such as renal involvement, which is not mentioned in this case.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Meningococcemia: This condition can present with a similar rash, but it is typically accompanied by fever, headache, and other systemic symptoms. Although the patient does not have these symptoms, meningococcemia is a medical emergency that requires prompt treatment.
- Testicular torsion: The scrotal swelling and pain could be indicative of testicular torsion, which is a surgical emergency. Although the patient's symptoms are more suggestive of HSP, testicular torsion must be ruled out.
- Rare diagnoses
- Polyarteritis nodosa: This is a rare form of vasculitis that can present with similar symptoms, including palpable purpura and joint pain. However, it often has additional symptoms such as hypertension and renal involvement.
- Rheumatoid arthritis: Although rare in adolescents, rheumatoid arthritis can present with joint pain and swelling. However, the presence of palpable purpura and scrotal swelling makes this diagnosis less likely.