Henoch-Schönlein Purpura Without Proven Immunoglobin A Deposition: A Diagnostic Distinction.

Henoch-Schönlein purpura (HSP), or immunoglobulin A (IgA) vasculitis (IgAV), is a small vessel vasculitis that is most commonly seen in children; it is classically characterized by IgA deposition within the renal mesangium, resulting in a wide range of symptoms: palpable purpura, arthralgia, gastrointestinal symptoms, renal involvement, and, in severe cases, pulmonary complications or intussusception. Diagnosis relies upon clinical symptoms, histopathology, and direct immunofluorescence (DIF) testing to differentiate HSP from other vasculitides. DIF typically reveals IgA deposits; however, negative DIF findings do not rule out the diagnosis, which indicates the need for an adaptable diagnostic approach. Groups such as the European League Against Rheumatism (EULAR) and the American College of Rheumatology (ACR) categorize positive IgA as supportive data for an HSP diagnosis but not as a necessity. We present the case of a 14-year-old male with progressive ascending palpable purpura, significant abdominal pain, and lower extremity edema. Histopathological analysis of the skin biopsy confirmed leukocytoclastic vasculitis (LCV); however, his DIF was negative for IgG, IgA, IgM, C3, and fibrinogen deposits. At the time of biopsy, his workup was significant for an isolated elevated alanine aminotransferase (ALT), but urinalysis and renal function testing were unremarkable. Despite a negative DIF, the patient's findings were clinically consistent with HSP, and hence, a diagnosis was made. He was started on a prednisone taper and supportive care for management. After initial improvement, he experienced a flare warranting an additional course of steroids, which improved his symptoms. This report underscores the diagnostic challenges associated with HSP, particularly with negative DIF. While DIF serves as a useful tool in the classification of certain vasculitides, its sensitivity is influenced by the biopsy site, lesion age, and degradation of immune complexes. Providers should maintain a high index of suspicion and carefully consider histopathologic findings and laboratory data when diagnosing HSP. Further research is needed to refine the diagnostic applicability of DIF and its association with disease severity and systemic involvement.