Small Vessel Vasculitis: Symptoms, Types, Rash, Treatment, and Pathology

Small Vessel Vasculitis:

• What is Small Vessel Vasculitis?
• Symptoms
• Types
• Rash
• Treatment
• Pathology

What is Small Vessel Vasculitis?

Small vessel vasculitis refers to a group of disorders characterized by inflammation of the smallest blood vessels in the body, such as capillaries, venules, and arterioles. This inflammation leads to vessel wall damage, narrowing, or even blockage, which disrupts blood flow to tissues and organs. The result can be a wide range of symptoms, depending on which organs are affected. Commonly involved areas include the skin, kidneys, nerves, and lungs.

Small vessel vasculitis can occur as a primary autoimmune disease or as a secondary condition triggered by infections, medications, or other underlying disorders. The immune system mistakenly attacks blood vessel walls, causing inflammation and tissue injury. Diagnosis often involves a combination of blood tests, biopsy, and imaging studies to identify the pattern of vessel involvement and to rule out systemic causes. Early recognition is important to prevent serious organ damage.

Symptoms

The symptoms of small vessel vasculitis can vary widely depending on the organs involved, but skin manifestations are among the most common. A characteristic finding is a rash called palpable purpura—small, raised red or purple spots usually appearing on the legs or buttocks. Patients may also experience fatigue, fever, joint pain, and general malaise. When internal organs are affected, symptoms can include abdominal pain, blood in urine, numbness, or shortness of breath.

Systemic involvement often causes more severe symptoms such as kidney inflammation (glomerulonephritis), nerve pain (neuropathy), or lung problems like coughing up blood. These symptoms arise because the inflamed vessels leak or become obstructed, leading to ischemia and tissue injury. Since vasculitis can mimic other diseases, a thorough clinical evaluation and laboratory workup are essential for accurate diagnosis and appropriate treatment.

Types

Small vessel vasculitis includes several specific diseases, often grouped by their underlying causes or immune mechanisms. The major types are:

• Leukocytoclastic vasculitis (LCV): Usually affects the skin and presents with palpable purpura.
• IgA vasculitis (Henoch-Schönlein purpura): Common in children and associated with kidney, joint, and gastrointestinal symptoms.
• ANCA-associated vasculitis (AAV): Includes granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA).
• Cryoglobulinemic vasculitis: Associated with hepatitis C and immune complex deposition.

Each type of small vessel vasculitis has distinct clinical and pathological features but shares the common process of immune-mediated injury to the vessel wall. Diagnosis often relies on antibody testing (e.g., ANCA, IgA, cryoglobulins) and biopsy findings to determine the specific subtype, which guides treatment.

Rash

One of the hallmark features of small vessel vasculitis is the development of a rash, typically described as palpable purpura. These are small, raised red or purple spots that do not blanch (fade) when pressed. They usually appear symmetrically on the lower extremities due to gravity and higher vascular pressure. The rash results from leakage of red blood cells through damaged vessel walls caused by inflammation.

In more severe cases, the rash may progress to ulceration, blistering, or necrosis, especially when deeper dermal vessels are involved. The rash can be accompanied by itching, tenderness, or pain. A skin biopsy is often performed to confirm the diagnosis and may show leukocytoclastic vasculitis—characterized by fragmented neutrophils around small vessels and immune complex deposition. Recognizing the rash early helps identify vasculitis before it progresses to internal organ involvement.

Treatment

Treatment for small vessel vasculitis depends on its underlying cause, severity, and organ involvement. Mild cases limited to the skin may resolve spontaneously or respond to anti-inflammatory medications like corticosteroids or nonsteroidal anti-inflammatory drugs (NSAIDs). For more severe or systemic cases, immunosuppressive therapy is often required to control the immune response and prevent organ damage.

Common treatments include corticosteroids (like prednisone), immunosuppressants such as azathioprine or methotrexate, and biologic agents like rituximab or cyclophosphamide for ANCA-associated vasculitis. Treating any underlying infection or discontinuing a triggering medication is also crucial. Long-term management may include regular blood work and imaging to monitor organ function and detect relapse early. A multidisciplinary approach involving rheumatologists, nephrologists, and dermatologists is often beneficial.

Pathology

The pathology of small vessel vasculitis involves immune-mediated inflammation targeting the endothelium of small blood vessels. On histologic examination, affected vessels often show fibrinoid necrosis, endothelial swelling, and infiltration of neutrophils or lymphocytes. The breakdown of neutrophils produces nuclear debris, known as leukocytoclasia, which is a key feature of leukocytoclastic vasculitis.

In immune complex–mediated types, deposition of immunoglobulins (such as IgA or IgG) and complement components can be detected using immunofluorescence. ANCA-associated vasculitis, on the other hand, typically lacks immune complex deposition and involves a different mechanism of neutrophil activation. Understanding the pathology is essential for differentiating between vasculitis subtypes and guiding targeted treatment. Biopsy remains the gold standard for confirming diagnosis and assessing disease activity.