Causes of Vasculitis
Vasculitis occurs either as a primary idiopathic condition (where the cause remains unknown) or secondary to identifiable triggers including infections, drugs, malignancies, and connective tissue diseases.
Primary (Idiopathic) Vasculitis
The primary systemic vasculitides represent a group of diseases where blood vessel inflammation occurs without a clearly identified external cause 1. These include:
- Large vessel vasculitis: Giant cell arteritis (GCA) and Takayasu arteritis (TAK), which affect the aorta and its major branches 2
- Medium vessel vasculitis: Polyarteritis nodosa and Kawasaki syndrome 2
- Small vessel vasculitis: ANCA-associated vasculitides including granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA) 2, 3
The exact pathophysiology of primary vasculitis remains incompletely understood, though recent investigations focus on autoimmune mechanisms, B lymphocyte dysfunction, and complement activation 4, 5.
Secondary Vasculitis
Infectious Causes
Infections are among the most common identifiable triggers for secondary vasculitis 1, 6:
- Viral infections: Hepatitis B virus causes polyarteritis nodosa (though incidence has decreased), hepatitis C virus is associated with mixed cryoglobulinemia in >80% of cases, HIV, cytomegalovirus, varicella-zoster virus, erythrovirus B19, and HTLV-1 6
- Bacterial infections: Staphylococcus aureus chronic nasal carriage is linked to disease relapses in GPA patients; Mycobacterium tuberculosis may induce Takayasu arteritis; Burkholderia species might be involved in giant cell arteritis; syphilis causes aortitis and cerebrovascular disease; rickettsial diseases 7, 6
- Fungal and parasitic infections: These typically cause vasculitis through direct vessel wall invasion or septic embolization, leading to mycotic aneurysms 6
Drug-Induced Vasculitis
Drug-induced vasculitis is actually the most common form of vasculitis overall 8. Various pharmaceutical agents can trigger blood vessel inflammation through immune-mediated mechanisms 8, 9. The key distinguishing feature is that withdrawal of the offending drug alone often induces prompt resolution of clinical manifestations, eliminating the need for immunosuppressive therapy 8.
Other Secondary Causes
- Connective tissue diseases: Rheumatoid arthritis, systemic lupus erythematosus, and other autoimmune conditions can present with vasculitis as a secondary manifestation 9
- Malignancy-associated vasculitis: Certain cancers can trigger paraneoplastic vasculitis 9
Clinical Pitfalls
The differential diagnosis between drug-induced and idiopathic vasculitis can be extremely difficult in individual patients 8. A careful medication history and temporal relationship between drug exposure and symptom onset is critical. Consider a trial of drug withdrawal before initiating aggressive immunosuppression when drug-induced vasculitis is suspected 8.
Recognizing an infectious origin is crucial because treatment strategies fundamentally differ from non-infectious forms 6. Antimicrobial therapy is mandatory for bacterial, fungal, or parasitic causes, while antiviral agents combined with plasma exchange are effective for HBV-related polyarteritis nodosa 6. Using cytotoxic immunosuppression for infection-related vasculitis can worsen outcomes, particularly in HIV-infected patients 6.