An 18-year-old woman comes to the emergency department for evaluation of a rash. The patient developed mild aches involving her knees and ankles 2 days ago. Before going to sleep last night, she noticed purplish spots around her right knee. Today, the rash involves both of the lower extremities. She has had no fever, weight loss, sore throat, abdominal pain, vomiting, or diarrhea. The patient has no chronic medical conditions and takes no medications. Temperature is 37 C (98.6 F), blood pressure is 146/90 mm Hg, pulse is 90/min, and respirations are 20/min. Cardiopulmonary examination is unremarkable. The patient has pain with passive range of motion of the knees and ankles. Skin examination is seen in the exhibit.
Laboratory results are as follows:
| Complete blood count | |
| Hemoglobin | 14 g/dL |
| Platelets | 260,000/mm3 |
| Leukocytes | 9,000/mm3 |
| Urinalysis | |
| Specific gravity | 1.016 |
| Protein | +2 |
Histologic examination of the rash is most likely to show which of the following?
IgA vasculitis (Henoch-Schönlein purpura) | |
Pathogenesis |
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Clinical |
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Diagnosis |
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This patient has a purpuric rash, arthralgia, and signs of renal disease (ie, hypertension, proteinuria), which are classic features of Henoch-Schönlein purpura (HSP), or IgA vasculitis. Other common findings can include colicky abdominal pain and hematuria.
HSP is an immune-mediated type III hypersensitivity reaction in which deposition of IgA immune complexes (which may form in response to a preceding upper respiratory infection) triggers complement activation and inflammation of small vessels throughout the body. Vasculitis within the papillary dermis manifests as nonthrombocytopenic palpable purpura on dependent areas, such as the buttocks and lower extremities. Histopathology shows leukocytoclastic vasculitis, in which small superficial blood vessels are damaged by perivascular neutrophilic inflammation, resulting in fibrin deposition in the vessel wall (ie, fibrinoid necrosis) and red blood cell extravasation. Neutrophil breakdown (leukocytoclasis) leads to the formation of perivascular nuclear debris. Immunofluorescence reveals IgA and C3 in the vessel walls.
HSP is usually benign and self-limiting, particularly in children. However, adults are at increased risk for renal complications, such as nephrotic syndrome and acute kidney injury.
(Choice A) Disseminated intravascular coagulation is characterized by abundant intravascular fibrin deposition (ie, fibrin thrombi) in the absence of vascular inflammation. It occurs most often in the setting of trauma, sepsis, or malignancy and presents with bleeding (eg, purpura) due to thrombocytopenia and coagulopathy. Although fibrin thrombi may be seen with HSP, extensive inflammatory infiltrate is also present.
(Choice B) Obliterative endarteritis with lymphocytes and plasma cells is seen with later-stage syphilis, which can cause arthralgias, renal abnormalities, and a rash; however, classic skin findings include scaly red/brown macules or papules that are typically diffuse and involve the palms and soles. In contrast, this patient has purpuric lesions localized to the lower extremities.
(Choice C) Perivascular necrotizing granulomas with eosinophilic infiltration are characteristic of eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome), a small- to medium-vessel vasculitis. It can cause renal, skin, and joint involvement later in life (eg, third to fourth decades) but initially presents with asthma symptoms, which are not seen in this patient.
(Choice E) Transmural granulomatous inflammation with fragmentation of elastic fibers is a typical finding of giant cell arteritis, seen in adults age >50. It involves medium/large arteries and most commonly presents with headache.
Educational objective:
Henoch-Schönlein purpura, or IgA vasculitis, classically presents with palpable purpura, with or without abdominal pain, arthralgias, and renal involvement. Histopathologic examination of the skin lesions reveals damaged small vessels with fibrinoid necrosis, perivascular neutrophilic inflammation, and nuclear debris (ie, leukocytoclastic vasculitis). Immunofluorescence reveals deposition of IgA and C3.