Henoch-Schonlein Purpura

(leukocytoclastic angiitis)

Within the general morphologic category of cutaneous, leukocytoclastic angiitis, Henoch-Schonlein purpura is a special variant in which immunofluorescent studies show deposits of IgA in the walls of lesional vessels. These deposits may be the marker for a local deposition of circulating immune complexes. The syndrome is manifested by symptomatology and signs that affect various organ systems, generally the skin, the gastrointestinal tract, and the kidney. Involvement of the kidneys may lead to progressive renal failure.

In the skin, the patterns are those of a classic leukocytoclastic angiitis. Perivascular and interstitial infiltrates of neutrophils are associated with deposits of fibrin (S8C15P2-1 & 2). Nuclear debris (leukocytoclasia) is a feature.

In the gastrointestinal tract, small vessels angiitis is again a feature.

In the kidneys, the changes are those of a glomerulonephritis with variable expressions of severity. The changes range from a proliferative mesangiopathy, to a focal, sclerosing mesangiopathy, to disseminated glomerular changes. In disseminated disease, crescents are found in association with the areas of focal sclerosis (S8C15P2-3 &4).

Behcet’s Syndrome

Behcet’s Syndrome is difficult to define histopathologically. Emphasis, in attempts to characterize the process, often has been placed on a vasculitic component. In addition, a high component of histiocytes often is emphasized in histologic descriptions. Clinically, a tendency for ulceration is emphasized.

Histologically, a collagenosis with lysis of collagen bundles of the reticular dermis is a prominent feature (S8C15P2-5). In this approach, the lesion shares qualities with a pyoderma that, in its interstitial infiltrates, is rich in histiocytes (S8C15P2-6 & 7). In keeping with the “pyodermatous” character of the process, some of the vessels in the lesions show thrombosis and fibrinoid necrosis (S8C15P2-8). Lymphocytes and histiocytes may cluster at the dermal-epidermal interface to produce mild lichenoid patterns (S8C15P2-9).

Jorizzo JI, et al: Mucocutaneous criteria for the diagnosis of Behcet’s disease: an analysis of clinicopathologic data from multiple international centers. J Am Acad Dermatol 1995;32: 968-76.

Polyarteritis Nodosa

Polyarteritis nodosa is a disease of muscular vessels. Generally, the affected vessels show transmural involvement and the character of the infiltrate relates to the age of the lesion. In the acute phase, fibrinoid necrosis and infiltrates of neutrophils are the chief features. The affected vessels may also undergo aneurysmal changes. Polyarteritis nodosa usually is a multi-system disease but, in some patients, the characteristic vascular changes may be limited to muscular vessels of the skin and subcutaneous tissue (S8C16P3-1-4).

Traumatic Erosive Dermatitis

(neurotic excoriation)

The neurotic excoriation usually is something more than an avulsion of epidermis from the dermis. It is, in large part, a reaction related to discharge of proteolytic enzymes into the dermis, near the dermal-epidermal interface. The lesion evolves as a thin zone of necrosis involving epidermis, papillary dermis, and a variable portion of the upper portion of the reticular dermis. Careful examination of the zone of necrosis will often reveal the ghost outline of keratinocytes of the epidermis in the most superficial portion of the inflammatory crust along the surface. The epidermis and papillary dermis undergo coagulation necrosis; the affected tissue is acellular. Neutrophils migrate into the area of necrosis and disintegrate; in the process, nucleic acid are impregnated in the zone of necrosis; the area of necrosis becomes intensely basophilic. Vessels within, and adjacent to, the area of necrosis oftens show fibrinoid necrosis and thrombosis. Viable neutrophils collect at the interface between viable and necrotic tissue. In this area, a defect eventually forms and the necrotic tissues separates from the underlying viable tissue; a sequestrum forms. The sequestrum eventually is sloughed along the surface. Before, or after, the slough, squamous epithelium extends along the interface; the defect is re-epithelialized, but the new epithelium sits upon a zone of cellular fibrous tissue, or upon the reticular dermis; the papillary dermis, as such, usually is lost with the slough (S8C16P3-5-7).

Livedo Vasculitis

Some vasculitic disorders are necrotizing, but do not evoke significant inflammatory infiltrates. The affected vessels usually are portions of the superficial vascular plexus of the dermis. Like many vasculitic processes, the lower extremities are a favored site. The necrotizing changes may be segmental; the affected vessels show fibrinoid necrosis of their walls; the vessels may be dilated and may contain thrombi (S8C16P3-8). Occlusion of the vessels produces varying degrees of ischemia; in more severe examples, a small infarct may be the result. Such lesions, on healing, are scarred and poorly vascularized. The late stage produces a clinical picture that has been characterized as atrophie blanche.

Granuloma Faciale

Granuloma faciale is a vasculitis that tends to be fixed in a limited anatomic distribution. It is expressed in variable patterns; the variations reflect the activity of the process at the time of biopsy. A lesion of granuloma faciale is cytologically pleomorphic. It also is vasoproliferative (vessels are increased in number in limited domains among hair follicles). The inflamed vessels, and their supporting fibrous matrix form islands which are separated from neighboring islands by hair follicles, and their perifollicular sheaths (S8C17P4-1 & 3). The domains - not the basic patterns - are comparable to the areas of telangiectasia and inflammation in telangiectatic variants of rosacea.

If examined during a period of active inflammation, vessels of the islands show focal areas of fibrinoid necrosis (S8C17P4-4, 6 & 7, and S8C18P5-4). These zones of fibrinoid are associated with infiltrates of neutrophils; some of the neutrophils show fragmentation of their nuclei (leukocytoclastic angiitis). Bouts of fibrinoid necrosis probably are episodic. The fibrinoid often is laminated; it undergoes repair by being converted to hyalin (toxic [laminated] hyalin) (S8C17P4-2). In the fibrous matrix (S8C17P4-5), which supports the newly formed vessels, inflammatory cells collect to form infiltrates. The interstitial infiltrates are pleomorphic; they are composed of lymphocytes, histiocytes, eosinophils, and plasma cells (S8C18P5-2 & 3). Some of the histiocytes contain hemosiderin granules.

The areas of inflammation and angiogenesis usually spare the papillary dermis and the perifollicular sheaths. A thin zone of reticular dermis, between the islands of inflammation and the papillary dermis, may also be spared. The zone between the islands and the epidermis has been characterized as a “grenz zone” (S8C17P4-5). Rarely, the infiltrates extend to the dermal-epidermal interface (S8C18P5-1).

Without attention to clinical characteristics, commonalities link the histologic patterns of leukocytoclastic angiitis, Wegener’s granulomatosis, Behcet’s syndrome, granuloma faciale, and erythema elevatum diutinum.