Vasculitis is an inflammatory process primarily occurring on the vessel wall leading to vessel wall destruction and subsequent hemorrhagic and ischemic events. Any organs rich in blood vessels could have lesions of vasculitis which may result in a fatal life-threatening condition when occurring in the major organs such as kidney, lung, gastrointestinal tract and central nervous system or follow a persistent morbidity with permanent sensory/motor disturbance of the extremities as well as refractory leg ulcers and toes gangrenes followed by a miserable outcome of amputation of extremities later.

Skin is the most common target organs for small vessel vasculitisfound in either primary systemic vasculitis (ANCA-associated vasculitis, polyarteritis nodosa) or secondary systemic vasculitis CTD-associated, drug-related, infection-related and neoplasm-related vasculitis) [1,2]. Vasculitis in skin (dermis to sub-cutis) could reflect a self-limited benign disease restricted to skin such as cutaneous leukocytoclasticangiitis and cutaneous polyarteritis nodosa (cutaneous arteritis) [1,3]or present as a significant component or even the first sign of many systemic vasculitic syndromes such as ANCA-associated primary vasculitic syndromes [1,2].

As clinical presentations of vasculitis in skin can be easily and accurately identified by naked eyes observation and palpable examination followed by a subsequently easier and relatively non-invasive skin biopsy for histopathological examination, the crucial diagnostic evidence for vasculitis, skin lesions with suspected vasculitis presentations provide an extremely valuable clue for making diagnosis of vasculitis easily and precisely when comparing to those vasculitis in either internal organs (kidney, lung, gastrointestinal tract, etc.) or peripheral nerves and muscles, an invasive and blind biopsy is usually needed for histopathological confirmation.

As vessels affected in cutaneous vasculitisranging from dermal small vessels to subcutaneous muscular vessels, cutaneous vasculitis presents as a mosaic of clinical findings [1,2] (Figure 1-5).

Figure 1: Rhuematoid vasculitis with hypocomplementemia and circulating immune-complexes. (A) Palpable purpura of the right leg with Köbner phenomenon (arrow), a sign of immune complex -mediated vasculitis. (B) Occurrence of left foot drop thereafter. (C) Histopathology of palpable purpura showing leukocytoclastic vasculitis of dermal small vessels. (D)Direct immunofluorescence showing IgM (arrow) vascular deposit.

Figure 2: Dermal-renal vasculitis in a case with a history of ventricular septal defect that was complicated by Streotpcoccal septicemia with glomerulo nephritis and persistent palpable purpura.Palpable purpura of the lower legs (B) Leukocytoclastic vasculitis of dermal vessels.

Figure 3: Dermal-renal vasculitis in a chronic hepatitis patient presenting as recurrent purpura of lower legs with cryoglobulinemia, hypocomplementemia and hematuria/ proteinuria. Palpable purpura of the lower legs (B) Histopathology of palpable purpura: Leukocytoclastic vasculitis of dermal vessels.

Figure 4: Cutaneous polyarteritis nodosa. Tender nodular/ infiltrated erythema ranging from 5-10mm in size mixed with livedo reticularis of the lower legs. Histopathology showing coronalike sub-intimal fibrinoid necrosis of the vessel wall with a marked mixed infiltrate of neutrophils , lymphocytes and histiocytes.

Figure 5: Cutaneous vasculitis in Behçet’s disease. (A) Erythema nodosum-like lesion of the lower legs. (B) Ileocecal ulcers complication. (C)Histopathology of erythema nodosum-like lesion showing subcutaneous phlebitis (D: higher magnification) with overlying lower dermal venulitis (E: higher magnification).

Cutaneous vasculitis of dermal small vessels clinically manifests most frequently as palpable purpure (Figures 1A-3A) , and less often infiltrated or swollen/elevated erythema, characterized by feature of leukocytoclastic vasculitis with a prominent infiltrate of neutrophils and nuclear debris (Figures 1C,2B and 3B), while vasculitis of subcutaneous small muscular vessels (arteritis (Figure 4B) or phlebitis (Figure 5B) ) is less commonly and clinically presents as nodular erythema (Figures 4A and 5A), livedo reticularis (Figures 4A), deep ulcers, or subcutaneous nodules.

Dermal small vessels vasculitis, the most common presentation of cutaneous vasculitis, can be found in both primary vasculitis syndromes including ANCA-associated vasculitis (microscopic polyangiitis, granunolomatosis with polyangitis, and eosinophilic granulomatosis with polyangiitis) [2,3] polyarteritis nodosa, Behçet disease and Cogan’s syndrome being listed in the category of variable vasculitis in 2013 updated definition of vasculitis [3] , IgA-vasculitis [4] and skin-limited cutaneous leukocytoclasticangiitis [3] and also secondary vasculitis syndromes including collagen–associated vasculitis (rheumatoid vasculitis (Figure 2) [5], lupus vasculitis, relapsing polyachondritis and Sjögren’s syndrome), drug-induced vasculitis, infection-induced vasculitis (streptococcal/ staphylococcal infection, (Figure 3) hepatitis C/B viral infection, (Figure 4) most often) , and relatively rare in paraneoplastic vasculitis.

Dermal small vessel vasculitis predominately affecting venules (venulitis) rather than the arterioles,is the most commonhistopathologicfeature of cutaneous vasculitis. However, in systemic vasculitis such asANCA-associated vasculitis not only venules but arteriolesmay be affected. Palpable purpuraon the lower legs is the most common clinical feature. (Figures 2-4) Because manyvasculitic disorders including both primary and secondary ones such as collagen disease-associated vasculitis (Figure 1) and infection-induced vasculitis (Figures 2,3) share the same histopathologic feature of dermal small vessel vasculitis and the similar cutaneous manifestations. A constellation of the clinical and laboratory evaluation isoften needed to make the final diagnosis [1,3] (Table 1) (Figures 5 and 6).

Table 1: Clinical, pathologic, and laboratory findings indicating a high probability of systemic disease

Coexistent dermal small vessel vasculitis and the overlying subcutaneous muscular vessel vasculitis is the characteristic features of systemic vasculitis such as ANCA-associated vasculitis [1,2], collagen disease [5] and Behcet’s disease [6,7] (Figure 5) Cogan’s syndrome, or infection, bowel inflammatory disease, drug and neoplasm-related vasculitis [4] (Figure 6).

Muscular vessels are those vessels with caliber larger than 100um of small to medium-sized muscular vessels (arteries and veins) found in lower dermis to subcutis. Small arteries or veins at dermo-subcutaneous junction ranging from 200um to 400um are the common vessels affected in either cutaneous polyarteritisnodosa (also known as cutaneous arteritis) [3], (Figure 4) a rather chronic disease limited to skin of the lower legs most often[1]or superficial (thrombo)phlebitis in either idiopathic ones or Behçet’s disease [6] (Figure 5)

As the crucial diagnosis of vasculitis is based on the histopathological findings, an appropriate skin biopsy is the key to obtaining a significant result for cutaneous vasculitis. Timing for a skin biopsy should not be performed after 48 hours for the appearance of the purpuric or infiltrated lesions and 72 hours for the appearance of the deep nodular erythematous lesions as the biopsy is poorly timed, the pathologic features of vasculitis may be absent. A biopsy extending to the subcutis should be taken from the most palpable purpuric lesions or the most tender, reddish nodular or infiltrated lesions. For purpuric lesions or infiltrated erythematous lesion smaller than 5mm in size, a 3 to 4 mm large punch biopsy extending to the subcutis will enable the histopathologic confirmation, while lesions of nodular erythema or infiltrated erythema larger than 5 mm in size, a spindle-shaped incisional biopsy extending to the subcutis with a 5 to 8 mm large tissue sample in size should be performed on the central lesions [1,4].

Cutaneous vasculitis could reflect a self-limited benign disease restricted to skin or present as a significant component or even the initial sign of many systemic vasculitic syndromes. As the merit of easy and precise diagnosis of vasculitis via skin biopsy, physicians who are familiar with the cutaneous manifestations of cutaneous vasculitis such as palpable purpura indicating dermal small vessel vasculitis while nodular lesions and livedo reticualris implicating deep dermal to subcutaneous arteritis/ phlebitis and the technique of skin biopsy, coupled with extra cutaneous clinical and laboratory evaluations (Table 1) will make the final diagnosis earlier for either systemic vasculitis with skin involve mentor skin-limited vasculitis.