TB Vasculitis: Vessel Involvement
Tuberculosis-associated vasculitis primarily affects small vessels (arterioles, capillaries, and venules), manifesting most commonly as cutaneous leukocytoclastic vasculitis with palpable purpura, particularly on the lower extremities. 1, 2
Primary Vessel Size Affected
Small vessel involvement is the hallmark of TB-associated vasculitis. The pathological process targets:
- Arterioles, capillaries, and venules in the dermis and subcutaneous tissue 3, 1
- Cutaneous manifestations present as leukocytoclastic vasculitis with palpable purpura, predominantly affecting the lower legs 1, 2
- Histopathologic features include angiocentric segmental inflammation, fibrinoid necrosis, and neutrophilic infiltrate around vessel walls with erythrocyte extravasation 3
Clinical Presentation Pattern
The typical presentation follows a distinct pattern:
- Palpable purpura on lower extremities is the classic finding, representing small vessel inflammation 1, 2
- Systemic symptoms including fever, myalgia, and weight loss often accompany the cutaneous findings 1, 2
- Subcutaneous nodules may occur, particularly in nodular vasculitis (erythema induratum of Bazin), which is characteristically associated with M. tuberculosis infection 4
Diagnostic Considerations
Tuberculosis should be considered as a causative agent when evaluating small vessel vasculitis, though it is a rare etiology. 1
Key diagnostic features include:
- Skin biopsy demonstrating leukocytoclastic vasculitis with small vessel involvement 1, 2
- Associated TB manifestations such as pulmonary involvement or tuberculous lymphadenitis 1, 2
- Resolution with anti-tuberculosis treatment confirms the causal relationship 1, 2
Important Clinical Pitfall
Do not confuse TB-associated vasculitis with drug-induced vasculitis from anti-tuberculosis medications. Anti-TB drugs (particularly rifampicin and ethambutol) can themselves cause leukocytoclastic vasculitis, presenting identically with small vessel involvement and palpable purpura 5. The timing of symptom onset relative to treatment initiation is critical for distinguishing these entities.
Vessel Size Classification Context
While TB primarily affects small vessels, understanding the broader vasculitis classification is helpful:
- Large vessels (aorta and major branches) are affected in giant cell arteritis and Takayasu arteritis 6
- Medium vessels (main visceral arteries) are involved in polyarteritis nodosa 6
- Small vessels (intraparenchymal vessels) are the target in TB-associated vasculitis, ANCA-associated vasculitis, and immune complex vasculitis 7, 8