Differential Diagnosis
The patient's presentation of leg pain, purplish rash, and laboratory results suggests a systemic condition. Here's a categorized differential diagnosis:
Single most likely diagnosis
- Henoch-Schönlein Purpura (HSP): The patient's symptoms, including leg pain, purplish rash, and hematuria (large blood on urinalysis), are consistent with HSP. The recent history of low-grade fever and cough may be related to an upper respiratory tract infection, which can trigger HSP.
Other Likely diagnoses
- Juvenile Idiopathic Arthritis (JIA): Although the patient's joints show no deformity, erythema, swelling, or warmth, JIA can present with systemic symptoms, including fever, rash, and leg pain.
- Vasculitis (e.g., Kawasaki disease): The patient's rash, fever, and leg pain could be indicative of a vasculitic process, although the lack of other typical symptoms (e.g., conjunctivitis, lymphadenopathy) makes this less likely.
Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Meningococcemia: The patient's rash and fever could be indicative of a life-threatening infection like meningococcemia, which requires prompt recognition and treatment.
- Sepsis: Although the patient's vital signs are not overtly concerning, the presence of fever, tachycardia, and leg pain warrants consideration of sepsis, particularly if the patient's condition deteriorates.
Rare diagnoses
- Hemophagocytic Lymphohistiocytosis (HLH): This rare condition can present with systemic symptoms, including fever, rash, and leg pain, although it is typically associated with more severe laboratory abnormalities (e.g., pancytopenia, elevated liver enzymes).
- Leukemia: Although the patient's symptoms are not typical for leukemia, it is essential to consider this diagnosis in the differential, particularly if the patient's condition worsens or if abnormal laboratory results are found (e.g., anemia, thrombocytopenia).