Markers of Cutaneous Polyarteritis Nodosa (PAN)
For patients with suspected cutaneous PAN, a deep-skin biopsy specimen (reaching the medium-sized vessels of the dermis) is essential for diagnosis, as this is more likely to capture the medium-sized vessels affected in this condition. 1
Diagnostic Features
Histopathological Markers
- Leukocytoclastic vasculitis in the small to medium-sized arterioles of the dermis 2
- Necrotizing arteritis with fibrinoid necrosis in the deep dermis or panniculus 3
- Inflammatory changes typically affecting a single artery in the deep dermis or subcutaneous tissue 3
- Focal panniculitis surrounding the involved artery (characteristic finding) 3
- Edema and inflammatory cell infiltration around affected vessels 3
Clinical Markers
- Tender subcutaneous nodules, particularly on the lower extremities 3, 4
- Livedo reticularis (retiform violaceous discoloration) 2, 4
- Subcutaneous ulcerations that may be slow to heal 2, 4
- Digital gangrene in severe cases 2
- Nodules at different stages of development simultaneously 3
- Residual violaceous livedoid color or pigmentation with retiform appearance that may persist for months or years 3
Laboratory Findings
- Mild to moderate elevation of inflammatory markers (less pronounced than in systemic PAN) 5
- Possible elevated antistreptolysin O (ASO) titers in some cases 3
Classification of Cutaneous PAN
Cutaneous PAN can be classified into distinct clinical phenotypes:
Mild cutaneous PAN:
- Female predominance (84.6%)
- Younger age (median 31 years)
- Lower doses of prednisolone typically required for treatment (median 20 mg/day) 5
Severe cutaneous PAN:
Distinguishing from Systemic PAN
Important distinctions from systemic PAN include:
- Absence of significant internal organ involvement 4
- More favorable prognosis 4
- Less severe elevation of inflammatory markers 5
- Younger age of onset compared to systemic PAN (which typically affects older individuals, median 71 years) 5
Diagnostic Approach
- Deep-skin biopsy is the gold standard for diagnosis, reaching medium-sized vessels of the dermis 1
- Superficial skin punch biopsies should be avoided as they may miss the deeper vascular involvement 1
- Abdominal vascular imaging may be considered to exclude systemic involvement 1
Common Pitfalls and Caveats
- Failure to obtain a deep enough biopsy specimen can lead to missed diagnosis 1
- Mistaking cutaneous PAN for systemic PAN can lead to unnecessary aggressive treatment 4
- Overlooking the possibility of progression from cutaneous to systemic disease (though uncommon) 4
- Underestimating the high relapse rate in severe cutaneous PAN (ulcer type), which may require more aggressive initial therapy 5
By recognizing these specific markers and obtaining appropriate diagnostic specimens, clinicians can accurately diagnose cutaneous PAN and distinguish it from systemic PAN, leading to appropriate treatment decisions that affect morbidity and mortality outcomes.