Review Question - QID 104252

Given this patient's presentation of palpable purpura on the lower extremities, abdominal pain, and diffuse arthritis following an upper respiratory infection, the most likely diagnosis is Henoch-Schonlein purpura (HSP). HSP is an IgA-mediated vasculitis.

HSP most commonly occurs in children. It typically presents between ages 3-15 and is self-limited in the majority of cases. HSP is frequently preceded by an upper respiratory infection and has the clinical manifestations of palpable purpura (without thrombocytopenia or coagulopathy), arthritis, abdominal pain, and renal disease. Purpura and arthritis are the most frequent initial presenting symptoms. The pathophysiology of HSP is the formation of IgA immune complexes within affected organs, accompanied by an inflammatory infiltrate of primarily neutrophils and monocytes.

Reamy et al. review the treatment of HSP. As HSP is self-resolving in the vast majority of cases, supportive treatment is typically the mainstay of management. NSAIDs or acetaminophen can be given for joint pain; however, NSAIDs have the potential to exacerbate gastrointestinal discomfort and should be avoided in patients who have disease with renal impairment. Steroids are the most appropriate initial treatment for patients with known renal involvement or severe extrarenal symptoms.

Chen and Mao indicate that, while the exact mechanisms have not been fully elucidated, HSP is an IgA vasculitis with the physical findings occurring as a result of the deposition of IgA immune complexes in the affected tissues. In renal injury secondary to HSP, the complexes deposit in the mesangium and activate the complement cascade. Additionally, as concurrent infection with streptococcus has been found in 20-30% of patients with HSP, it has been postulated that group A streptococcal antigens may be responsible for HSP in some cases.

Figure A shows the typical distribution of the palpable purpura found in HSP. It is symmetrically distributed on the lower extremities. The buttocks is typically affected in toddlers. Illustration A demonstrates a close-up view of palpable purpura located on the lower extremities of a child affected with HSP.

Incorrect Answers:
Answer 1: Exotoxins are implicated in the pathophysiology of toxic shock syndrome.
Answer 2: Histamine release is implicated in the development of urticaria.
Answer 3: Immune-mediated platelet destruction is one process responsible in the development of immune thrombocytopenic purpura. As this patient has a normal platelet count, this diagnosis is less likely.
Answer 5: Anti-neutrophil cytoplasmic antibodies are found in granulomatosis with polyangiitis.