Pigmented Purpuric Dermatosis (Capillaritis)
The most likely diagnosis is pigmented purpuric dermatosis (PPD), a chronic capillaritis characterized by reddish-brown macules with non-palpable purpura that typically begins on the lower extremities and can spread to other body areas over months to years. 1, 2
Clinical Features Supporting This Diagnosis
The patient's presentation demonstrates the hallmark characteristics of PPD:
- Reddish-brown macules with multiple non-palpable purpura represent the classic "cayenne pepper-like spots" that define this condition 1, 2
- Initial foot involvement with gradual spread to thighs, back, and abdomen over 2 years matches the typical chronic, progressive pattern of PPD 3, 4
- Pruritic nature is consistent with PPD, which can be asymptomatic or pruritic 2, 5
- Non-palpable purpura distinguishes this from vasculitic conditions where purpura is typically palpable 1
Distinguishing From Other Conditions
The clinical presentation effectively rules out several alternatives:
- Not Stevens-Johnson Syndrome/TEN: Absence of mucosal involvement, blistering, or epidermal detachment excludes this diagnosis 6
- Not pyoderma gangrenosum: Lacks the deep excavating ulcerations and pustular evolution characteristic of PG 6
- Not erythema nodosum: The lesions are flat macules rather than raised, tender subcutaneous nodules 6
- Not bullous pemphigoid: Absence of bullae and the chronic non-blistering course excludes BP 6
Diagnostic Confirmation Without Biopsy
While biopsy would definitively show perivascular lymphocytic infiltrate with erythrocyte extravasation and hemosiderin deposition 1, 2, the clinical diagnosis can be made based on:
- Dermoscopic examination revealing red globules, red dots, and coppery brown background—findings present in 100% and 72% of PPD cases respectively 2
- Distribution pattern starting distally and spreading proximally over years 3, 4
- Absence of systemic symptoms or laboratory abnormalities that would suggest vasculitis or other systemic disease 1, 5
Clinical Subtypes and Variants
PPD encompasses several subtypes, though strict classification can be difficult:
- Purpura annularis telangiectodes of Majocchi presents with annular hyperpigmented patches, which may develop in this patient 3
- Atypical presentations are well-recognized, and the extensive distribution to trunk and upper body represents an uncommon but documented pattern 5
Management Approach
Phototherapy (narrowband UVB or PUVA) represents the most effective treatment option, with documented excellent response rates in published cases. 3
Additional therapeutic considerations include:
- Topical corticosteroids for symptomatic relief of pruritus, though they do not alter disease course 4
- Vitamin C supplementation may help reduce residual pigmentation after active lesions resolve 4
- Avoidance of potential triggers including certain medications, though causative factors remain poorly understood 4, 5
Important Clinical Caveats
- Biopsy is indicated if the diagnosis remains uncertain, lesions become atypical, or treatment fails, as other conditions can occasionally mimic PPD 1, 5
- The condition is chronic and relapsing, so patients should be counseled about the expected prolonged course and potential for recurrence 3, 4
- Upper extremity and truncal involvement is less common than lower extremity disease, but when present, does not change the diagnosis or management 1, 5