What is the diagnosis and treatment for progressive purpuric lesions spreading over the body?

Progressive Purpuric Lesions: Diagnosis and Management

The most likely diagnosis is pigmented purpuric dermatosis (PPD), specifically Schamberg's disease, given the chronic progressive course over six months with spreading purpuric lesions in the absence of systemic symptoms, and treatment should begin with narrow-band UVB phototherapy. 1

Differential Diagnosis Algorithm

Critical Life-Threatening Conditions to Rule Out First

Immediately assess for systemic involvement to exclude conditions requiring urgent intervention:

• Check vital signs and assess for fever, hypotension, or signs of sepsis - Rocky Mountain Spotted Fever (RMSF) can present with progressive purpuric rash but typically includes fever, headache, and rapid progression over days (not months), with case-fatality rates of 5-10% if untreated 2
• Examine for skin tenderness, pain, and Nikolsky sign - Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) presents with tender skin and mucosal involvement, but progression occurs over days, not months 3
• Assess for palpable purpura versus non-palpable purpura - Palpable purpura suggests vasculitis (Henoch-Schönlein purpura, cutaneous small vessel vasculitis), while non-palpable purpura with cayenne pepper-like appearance suggests PPD 4, 5, 6

Key Distinguishing Features

For a six-month progressive course without systemic symptoms, consider:

• Pigmented purpuric dermatoses (PPD) - Chronic benign condition characterized by petechiae, purpura, and orange-brown speckled "cayenne pepper-like" discoloration, typically affecting lower extremities and spreading proximally 6
• Henoch-Schönlein purpura (HSP) - Requires palpable purpura PLUS at least one of: renal involvement (hematuria/proteinuria), arthralgia/arthritis, or abdominal pain 4
• Cutaneous small vessel vasculitis - Presents with palpable purpura, often secondary to drugs, infection, or collagen vascular disease 5

Essential Diagnostic Workup

Immediate Laboratory Testing

Order the following tests to guide diagnosis:

• Complete blood count with platelet count - Essential to exclude thrombocytopenic purpura (platelets typically <30,000 cause purpura) 7
• Peripheral blood smear - Confirms platelet count and excludes other hematologic causes 7
• Urinalysis with microscopy - Look for proteinuria, red blood cell casts, and dysmorphic RBCs to assess for glomerulonephritis in HSP 4
• Basic metabolic panel - Assess BUN, creatinine for renal involvement 4
• Coagulation studies - If purpura fulminans suspected (though unlikely given chronic course) 8

Definitive Diagnostic Test

Perform skin biopsy with both H&E and direct immunofluorescence - This is crucial for definitive diagnosis and should not be delayed 3, 7

• PPD shows: Perivascular lymphocytic infiltrate with extravasated red blood cells and hemosiderin deposition, without true vasculitis 6
• Vasculitis shows: Leukocytoclastic vasculitis with fibrinoid necrosis of vessel walls 5, 6
• HSP shows: IgA deposition on direct immunofluorescence 4

Treatment Based on Diagnosis

For Pigmented Purpuric Dermatosis (Most Likely)

Initiate narrow-band UVB phototherapy as first-line treatment:

• Treatment protocol: Three times weekly until clearance (typically 24-28 treatments), followed by maintenance therapy twice weekly for 3 weeks, then once weekly for 3 weeks 1
• Expected outcomes: Successful clearance achieved in all patients in published series, with only occasional flares after discontinuation that respond to retreatment 1
• Alternative options if phototherapy unavailable: Colchicine 1 mg/day for at least 6 months for persistent purpura and pain 4

For Henoch-Schönlein Purpura (If Confirmed)

Treatment depends on organ involvement:

• For cutaneous and joint symptoms only: Oral prednisone 1-2 mg/kg daily for two weeks may provide symptomatic relief 4
• For renal involvement with persistent proteinuria: ACE inhibitors or ARBs as first-line therapy 4
• For persistent proteinuria >1 g/day per 1.73 m² after ACE inhibitor/ARB trial: 6-month course of corticosteroid therapy 4
• For crescentic HSP with nephrotic syndrome: Steroids plus cyclophosphamide 4

For Cutaneous Small Vessel Vasculitis

Management approach:

• Identify and discontinue any potential causative medications 5
• For idiopathic or persistent cases: Dapsone, colchicine, or systemic corticosteroids 5

Critical Pitfalls to Avoid

Do not delay skin biopsy waiting for laboratory results - Histopathology is crucial for definitive diagnosis and guides treatment 3

Do not transfuse platelets for isolated thrombocytopenia without active bleeding - Not indicated in immune thrombocytopenic purpura or vasculitic processes 3

Do not assume benign disease without proper workup - While PPD is benign, vasculitis and HSP require monitoring for systemic complications, particularly renal involvement 4, 5

Do not miss renal involvement in HSP - Monitor blood pressure and perform serial urinalysis, as persistent hematuria and proteinuria indicate ongoing disease activity requiring treatment 4

Monitoring Protocol

For PPD: Clinical photography to document extent and response to treatment 3

For HSP: Serial urinalysis and blood pressure monitoring to detect renal involvement early 4

For any vasculitis: Daily assessment of body surface area involvement and progression of lesions 3