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© Dirk Biddle
Where a discharge (exudation) of neutrophils (and sometimes fibrin) around the dermal venules, with nuclear dust (fragments of leucocytes) and the escape of red blood cells into the surrounding tissue (extravasation) is present, the vasculitis condition may be described as leukocytoclastic. Leukocytoclastic vasculitis is usually limited to the skin but may involve other tissues. Fibrinoid necrosis is a hallmark of this type of vasculitis. Fibrinoid necrosis occurs in the wall of blood vessels when the vessel’s endothelium and smooth muscle cells are injured and dying. Areas of fibrinoid necrosis stain brightly eosinophilic under a microscope and indicate an allergic hypersensitivity component. If there is an allergic hypersensitivity component, eosinophils may also be present. If the vasculitis is intense, a hemorrhagic bullous eruption may occur, and rarely, cutaneous infarction. Over time the neutrophil exudation may give way to mononuclear infiltrates (eg; macrophages). Cryoglobulins and arthralgia may be risk factors for this particular vasculitis condition.
Leukocytoclastic vasculitis has also been known as hypersensitivity vasculitis, allergic vasculitis, hypersensitivity angiitis and allergic angiitis. It is not a specific disease but rather a clinicopathologic entity affecting the small vessels of the skin. It may however present as a vasculitis condition in its own right (as in Cutaneous leukocytoclastic angiitis) or as a comorbid condition associated with primary vasculitides such as Behcet’s disease, Henoch-Schönlein purpura and Polyarteritis nodosa. Secondary vasculitides due to drugs, infections, or in association with connective tissue diseases, Serum sickness, Systemic lupus erythematosus, celiac disease, inflammatory bowel disease, cystic fibrosis, Sjogren's disease, subcorneal pustular dermatosis, sarcoidosis, pyoderma gangrenosum, Wiskott-Aldrich syndrome, alpha-1 antitrypsin deficiency and Urticarial vasculitis also may present with a leukocytoclastic vasculitis component (1).
Leukocytoclastic vasculitis is thus characterised by the predominance of neutrophils, as opposed to lymphocytic vasculitis, characterised by a predominance of lymphocytes (usually T-cells) and Eosinophilic vasculitis, characterised by a predominance of eosinophils (see the following two sections).
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1. (http://www.thedoctorsdoctor.com/diseases/leukocytoclastic_vasculitis.htm).
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Exudation: The act of exuding; sweating; a discharge of humors, moisture, juice, or gum, as through pores or incisions; also, the substance exuded. 'Resins, a class of proximate principles, existing in almost all plants and appearing on the external surface of many of them in the form of exudations.' (OMD)
Fibrin: The insoluble protein formed from fibrinogen by the proteolytic action of thrombin during normal clotting of blood. Fibrin forms the essential portion of the blood clot. (OMD)
Dermal: Of or pertaining to the skin
Nuclear Dust: Fragments of cell nucleii. When a cell dies, its nucleus shrivels and becomes composed entirely of heterochromatin. Later the nucleus can break up into fragments ('nuclear dust') or even disappear
Red Blood Cells: Cell specialised for oxygen transport (erythrocyte), having a high concentration of haemoglobin in the cytoplasm (and little else). Biconcave, anucleate discs, 7nm diameter in mammals, nucleus contracted and chromatin condensed in other vertebrates. (OMD)
Extravasation: A discharge or escape, as of blood, from a vessel into the tissues
Fibrinoid Necrosis: Necrosis in which the necrotic tissue has some staining reactions resembling fibrin and becomes deeply homogenous and refractile. (OMD)
Smooth Muscle Cells: Smooth muscle tissue in vertebrates is made up from long tapering cells that may be anything from 20-500m long. Smooth muscle is generally involuntary and differs from striated muscle in the much higher actin/myosin ratio, the absence of conspicuous sarcomeres and the ability to contract to a much smaller fraction of its resting length. Smooth muscle cells are found particularly in blood vessel walls, surrounding the intestine (particularly the gizzard in birds) and in the uterus. The contractile system and its control resemble those of motile tissue cells (e.g. Fibroblasts, leucocytes) and antibodies against smooth muscle myosin will cross react with myosin from tissue cells, whereas antibodies against skeletal muscle myosin will not. (OMD)
Allergic Hypersensitivity: The manifestations of a particular allergic reaction depend on which of the immune mechanisms predominates in the response. Based on this criterion, immunologists use the Gell-Coombs classification system to recognize four types of hypersensitivity reactions. Types I, II, and III involve antibody-mediated mechanisms and are of rapid onset. The type IV reaction stems from cell-mediated mechanisms and has a delayed onset. It should be noted that the categorization, though useful, is an oversimplification and that many diseases involve a combination of hypersensitivity reactions. (Britanica, 2002)
Bulla: A bleb; a vesicle, or an elevation of the cuticle, containing a transparent watery fluid. (OMD) Plural = Bullae
Cryoglobulin: Any of several proteins (immunoglobulins) similar to gamma-globulins (as in molecular weight) that precipitate - usually in the cold - from blood serum especially in pathological conditions (as multiple myeloma) and that redissolve on warming. (M+)
Arthralgia: Pain in a joint. (OMD)