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CUTANEOUS SMALL - VESSEL VASCULITIS

(CSVV, leukocytoclastic vasculitis)

General aspects

Many clinically diverse disorders include histologic features of small-vessel vasculitis (vessel-directed inflammation), including erythema multiforme (Ch.11), erythema elevatum diutinum (this chapter), pityriasis lichenoides acuta (Ch.33), drug-induced vasculitis, occlusive vasculitis, and HSP.

    While many of these are morphologically distinct disorders, most CSVV presents with a clinical picture that does not in itself identify a specific cause. The features of palpable purpura, in some cases with associated urticarial lesions, pustules, or necrotic areas (Figs 14.14 – 14.20), are common to a wide range of disorders and etiologies. This section addresses the causes, relevant investigations, and main differential diagnoses of this constellation of features, in which the histologic correlate is a leukocytoclastic small-vessel vasculitis (leukocytoclasis implies the presence of fragmented nuclear remnants of neutrophil polymorphs in the perivascular and vessel wall infiltrate).

Figure 14.14 Henoch–Schönlein purpura: a typical pattern of palpable purpura at a typical site on the lower legs. This cannot be distinguished with certainty from other causes of small-vessel leukocytoclastic vasculitis on purely clinical grounds.

Figure 14.15 A more widespread semiconfluent pattern of palpable purpura. This urticated erythematous appearance is suggestive that Henoch–Schönlein purpura is the cause.

Figure 14.16 Henoch–Schönlein purpura affecting the genitalia. Lesions of buttocks and genitalia, along with lower leg lesions, are common in this disorder. (Courtesy of Dr. G. Dawn.)

Figure 14.17 Close-up view of purpuric spots in a case of Henoch–Schönlein purpura. Note the reticulate pattern.

Figure 14.18 Henoch - Schönlein purpura demonstrating the retiform pattern of purpura. This occurs in other disorders, such as cryoglobulinemia, but the combination of retiform purpura with early inflammation is strongly suggestive of IgA-mediated vasculitis.

Figure 14.19 Henoch– Schönlein purpura on the feet, with a pustule.

Figure 14.20 (a,b) Both annular lesions (a) and bullae may occur in several types of cutaneous small-vessel vasculitis, as shown here. (Panel b shows the same patient as in Fig. 14.1.)

Etiology and pathogenesis

The main causes of CSVV are listed in Table 14.5.

Figure 14.21 Bywater lesion of rheumatoid disease. This occurs around the nail fold orfinger pulps as a deep nodule, which may become crusted. Histologically, there is a leukocytoclastic vasculitis withfibrinoid degeneration.

Figure 14.22 Rheumatoid leg ulcers. These are punched out and painful, without venous stasis changes, and therefore have the clinical appearance of arterial ulceration (see also Ch. 15).

Clinical

The skin lesions in most of these are similar. They occur primarily in dependent areas, mainly the lower legs. Individual lesions are usually a few millimeters to 1cm in diameter, purpuric, often palpable, and may be necrotic. Blisters, usually hemorrhagic, may occur, and pustules (the latter especially in bacteremic causes of vasculitis). Larger necrotic areas may develop, especially around the ankles.

    The presence of inflammation in early lesions helps to distinguish processes with primary vessel wall injury, compared with occlusive microvascular occlusion disorders. A primary vasculitis causes inflammation, with purpura as a secondary event, whereas inflammation occurs as the secondary event in microvascular occlusion disorders. Vasculitis lesions of any size are therefore palpable from the outset, whereas lesions due to microvascular occlusion initially consist of ‘bland' non-inflamed lesions, often in a reticulate pattern, even though they may become edematous or inflamed later. Evaluation of early lesions is therefore important in directing the most profitable avenues of investigation. The combination of early inflammation and a reticulate or retiform patterning (Figs 14.17 and 14.18) is suggestive of IgA-mediated vasculitis (HSP).

Differential diagnosis

The main differential diagnosis issue is between the different causes of CSVV, and the distinction from disorders causing vascular occlusion.

Differentials of a small-vessel vasculitic process include the following.

Treatment of CSVV

The same principles apply to most causes of CSVV and to many of the specific patterns of vasculitis discussed later. Investigations should be performed to identify a treatable cause (see earlier text and Tables 14.3 and 14.4), the differential diagnosis should be addressed, and any identified cause such as medications should be specifically addressed. Rest, with elevation of the legs, may be sufficient therapy in many patients with mild vasculitis, and simple analgesics may be all that is required for arthralgia. Systemic corticosteroids are useful for arthralgia if sufficiently severe, and variably useful for renal or skin lesions; for cutaneous disease, this approach is usually reserved for more active necrotic or ulcerated lesions. Dapsone and colchicine are also useful as first-line or steroid-sparing therapy; azathioprine may be used for its steroid-sparing effect.

White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.