USMLE Guide: Henoch-Schönlein Purpura

Introduction

Henoch-Schönlein Purpura (HSP), also known as IgA vasculitis, is a systemic small vessel vasculitis that primarily affects children. This USMLE guide aims to provide a comprehensive overview of HSP, including its clinical presentation, pathophysiology, diagnosis, and management.

Clinical Presentation

1. Skin Manifestations

   • The hallmark feature of HSP is palpable purpura, typically on the lower extremities and buttocks.
   • Purpura may be preceded by erythematous macules or papules.
   • It may also involve the upper extremities, face, and trunk.
   • Lesions are non-thrombocytopenic and do not blanch on pressure.

2. Joint Involvement

   • Arthritis or arthralgia is present in the majority of cases.
   • Most commonly affects the knees and ankles.
   • Joint symptoms are migratory and self-limited.

3. Gastrointestinal (GI) Symptoms

   • Abdominal pain is a common complaint.
   • May be associated with nausea, vomiting, or bloody stools.
   • Intussusception, although rare, can occur as a complication.

4. Renal Involvement

   • Hematuria and proteinuria are common, often manifesting as tea-colored urine.
   • Renal involvement may range from mild to severe, including nephritis and nephrotic syndrome.

Pathophysiology

1. Immunologic Mechanisms

   • HSP is thought to be an immune complex-mediated vasculitis.
   • Deposition of IgA immune complexes in small vessels triggers an inflammatory response.
   • Complement activation and neutrophil infiltration contribute to vascular damage.

2. Precipitating Factors

   • HSP is often preceded by an upper respiratory tract infection or other viral illness.
   • Certain drugs, insect bites, and vaccinations have also been associated with HSP.

3. Genetic Predisposition

   • HSP has a higher incidence in individuals with a family history of the disease.
   • Genetic factors may influence susceptibility to immune complex formation.

Diagnosis

1. Clinical Evaluation

   • Diagnostic criteria include palpable purpura with at least one of the following:
     • Abdominal pain
     • Arthritis or arthralgia
     • Renal involvement (hematuria, proteinuria)
   • HSP should be considered in children with these findings.

2. Laboratory Investigations

   • Urinalysis: Presence of hematuria and/or proteinuria.
   • Elevated acute phase reactants (e.g., ESR, CRP).
   • IgA levels may be elevated, but this is not specific for HSP.

3. Renal Biopsy

   • Reserved for cases with severe renal involvement or atypical presentation.
   • Demonstrates mesangial IgA deposition and variable degrees of glomerular injury.

Management

1. Supportive Care

   • Symptomatic treatment includes rest, hydration, and pain relief.
   • Joint symptoms can be managed with nonsteroidal anti-inflammatory drugs (NSAIDs).
   • Severe GI involvement may require nasogastric decompression or surgical intervention.

2. Renal Involvement

   • Mild cases often resolve spontaneously, requiring close monitoring.
   • Severe nephritis or nephrotic syndrome may warrant corticosteroid therapy.
   • ACE inhibitors or angiotensin receptor blockers (ARBs) may be used for proteinuria.

3. Complications

   • Intussusception: Requires immediate surgical consultation.
   • Renal involvement: Long-term follow-up for monitoring renal function and blood pressure.

Conclusion

Henoch-Schönlein Purpura is a self-limiting vasculitis primarily affecting children. Understanding its clinical presentation, pathophysiology, diagnosis, and management is essential for medical professionals. This USMLE guide provides a comprehensive overview to aid in the preparation for exams or clinical practice.