Also known as gyrate erythema, this disorder represents a hypersensitivity reaction manifesting as arcuate and polycyclic areas of erythema. The condition has been categorized into superficial and deep variants. The deep form is characterized clinically by annular areas of palpable erythema with central clearing and absence of surface changes. The superficial variant differs only by the presence of a characteristic trailing scale, a delicate annular rim of scale that trails behind the advancing edge of erythema. Small vesicles may occur. The lesions may attain considerable size (up to 10 cm across) over a period of several weeks, may be mildly pruritic, and have a predilection for the trunk and proximal extremities. Erythema annulare centrifugum can be considered a reactive phenomenon, and has been associated with a variety of disparate conditions including pregnancy, surgical procedures, breast cancer, lymphoma, leukemia, herpes zoster, medication reactions, as well as others. Most cases resolve spontaneously within 6 weeks; however, the condition may persist for years.

In the classic deep or indurated type, a perivascular lymphocytic infiltrate characterized by a tightly cuffed “coat-sleeve–like” pattern is present in the middle and lower portions of the dermis. In the superficial variant, there is a superficial perivascular tightly cuffed lymphohistiocytic infiltrate with endothelial cell swelling and focal extravasation of erythrocytes in the papillary dermis, and focal epidermal spongiosis and parakeratosis can be seen. Erythema chronicum migrans (ECM) is an important differential, but often presents with plasma cells as well as lymphocytes and is therefore discussed also in VA4.

Also known as lichen urticatus, this condition is the result of hypersensitivity to bites from certain insects, especially mosquitoes, fleas, and bedbugs. One observes edematous papules and papulovesicles, which, because of severe itching, usually are excoriated. The eruption is more common in children than adults, and, if caused by mosquitoes, is limited to the summer months.

The stratum malpighii shows intercellular and intracellular edema and occasionally a spongiotic vesicle. A predominantly lymphocytic infiltrate is present around the vessels of the dermis, often extending into the lower dermis and containing a significant admixture of eosinophils.

Urticaria is characterized by the presence of abrupt onset, transient and recurrent wheals, which are raised erythematous and edematous areas of skin that are often pruritic. When large wheals occur and the edema extends to the subcutaneous or submucosal tissues, the process is referred to as angioedema. Acute episodes of urticaria generally last only several hours. When episodes of urticaria last up to 24 hours and recur over a period of at least six to eight weeks, the condition is considered chronic urticaria. The various causes of urticaria include soluble antigens in foods, drugs, insect venom; contact allergens; physical stimuli such as pressure, vibration, solar radiation, cold temperature; occult infections and malignancies; and some hereditary syndromes, but in many cases the cause remains undetermined.

In acute urticaria, the prominent feature is interstitial dermal edema, with dilated lymphatics and venules with endothelial swelling, and a paucity of inflammatory cells. In chronic urticaria, interstitial dermal edema and a perivascular and interstitial mixed-cell infiltrate with variable numbers of lymphocytes, eosinophils, and neutrophils are present.

Pruritic urticarial papules and plaques of pregnancy (PUPPP) is a fairly common entity that has a predilection for primigravidas in the third trimester of pregnancy (5). It can also occur directly post partum. PUPPP is associated with excessive maternal weight gain and multiple pregnancies. The rash usually starts on the abdomen and is composed of intensely pruritic erythematous urticarial papules, which may be surmounted by vesicles. The proximal parts of the extremities are also affected. There is no increased incidence of the rash in subsequent pregnancies. Typically lesions begin within striae distensae, and sparing of the umbilical area is a characteristic finding (as opposed to pemphigoid gestationis. The rash usually involutes spontaneously after delivery. Fetal outcome appears to be unaffected. The skin of the newborn child is unaffected (6).

Microscopic findings most commonly show a superficial and mid-dermal perivascular lymphohistiocytic infiltrate with variable numbers of eosinophils and neutrophils together with edema of the superficial dermis. Epidermal involvement is variable and consists of focal spongiosis with exocytosis, parakeratosis, and mild acanthosis.

The two fundamental pathologic changes in syphilis are (1) swelling and proliferation of endothelial cells and (2) a predominantly perivascular infiltrate composed of lymphoid cells and often plasma cells. However, plasma cells and endothelial swelling are not invariably present. Frank necrotizing vasculitis is distinctly unusual. In late secondary and tertiary syphilis,
there are also granulomatous infiltrates of epithelioid histiocytes and giant cells.

Biopsies generally reveal psoriasiform hyperplasia of the epidermis with spongiosis and basilar vacuolar alteration, exocytosis of lymphocytes, spongiform pustulation, and parakeratosis. The parakeratosis may be patchy or broad, with or without intracorneal neutrophilic abscesses. Scattered necrotic keratinocytes may be observed. Ulceration is not usual except in lues maligna. The dermal changes include marked papillary dermal edema and a perivascular and/or periadnexal and often lichenoid infiltrate that may be lymphocyte predominant, lymphohistiocytic, histiocytic predominant, or frankly granulomatous and that is of greatest intensity in the papillary dermis and extends as loose perivascular aggregates into the reticular dermis. In a few cases, atypical-appearing nuclei may be present and may suggest the possibility of lymphoma. Neutrophils are not infrequent and may permeate the eccrine coil to produce a neutrophilic eccrine hidradenitis. Granulomatous inflammation develops after a few months. A silver stain is positive for spirochetes in about a third of the cases. Silver stains can be difficult to interpret because of high background. In addition, positive results do not necessarily indicate the presence of Treponema Pallidum as a silver stain is not specific for this organism. Immunohistochemistry using antibodies directed against Treponema Pallidum Antigen have been shown to be more sensitive than silver stains and reflect a new standard for adjunct histological testing. PCR analysis is another technique which is valuable for the detection of Treponema
Pallidum (8,9,10). The organisms are seen in the epidermis, follicular epithelium, and blood vessels. Lesions of condylomata lata show all of the aforementioned changes, but with more florid epithelial hyperplasia and intraepithelial microabscess formation.

Erythema chronicum migrans is the distinctive cutaneous manifestation of stage I Lyme disease and represents the site of primary tick inoculation. The lesion starts as an area of scaly erythema or a distinct
red papule within 3 to 30 days after the tick bite, before spreading centrifugally with central clearing after a few weeks, occasionally reaching a diameter of 25 cm. Average lesional duration is a few weeks but in some cases, lesions may persist for as long as 12 months. The lesions may be solitary or multiple, the latter reflecting hematogenous dissemination of the spirochete, which may be accompanied by fever, fatigue, headaches, cough, and arthralgias.

An intense superficial and deep angiocentric, neurotropic, and eccrinotropic infiltrate predominated by lymphocytes with a variable admixture of plasma cells and eosinophils is the principal histopathology. Plasma cells have been identified most frequently in the peripheries of lesions of erythema chronicum migrans, whereas eosinophils are identified in the centers of the lesions. Not infrequently, these florid dermal alterations are accompanied by eczematous epithelial alterations, and interstitial infiltration of the reticular dermis with a concomitant incipient sclerosing reaction. A Warthin-Starry stain may be positive, especially if taken from the advancing border of the lesion.

The clinical manifestations include crops of asymptomatic, slightly raised, yellowish red papules that gradually develop an atrophic porcelain-white center. These papules tend to affect the trunk and proximal extremities. Degos initially described a cutaneointestinal syndrome, in which distinct skin findings (“drops of porcelain”) were associated with recurrent attacks of abdominal pain that often ended in death from intestinal perforations. He chose the name malignant atrophic papulosis (MAP) to emphasize the serious clinical course of the disease. It is nowadays believed that MAP is a clinicopathologic reaction pattern that can be associated with a number of conditions that are not always lethal. Lesions similar if not identical to MAP have been noted, in particular, in connective tissue diseases such as lupus erythematosus, dermatomyositis, and progressive systemic sclerosis, in atrophie blanche, and in Creutzfeldt–Jakob disease. On dermoscopy, a telangiectatic rim can be seen at the periphery of lesions, which can help differentiate this entity from other skin disorders (13).

Although the pathogenesis of Degos’ syndrome is poorly understood, a thrombotic vasculopathy is a characteristic associated finding. A typical lesion shows a wedge-shaped area of altered dermis covered by atrophic epidermis with slight hyperkeratosis. Dermal alterations may include frank necrosis, but more common are edema, extensive mucin deposition, and slight sclerosis. There may be a sparse perivascular lymphocytic infiltrate but the vessel walls are not inflamed. Typically, vascular damage is noted in the vessels at the base of the “cone of necrobiosis.” This damage may be limited to endothelial swelling, but more characteristically, intravascular fibrin thrombi may be noted, suggesting that the dermal and epidermal changes result from ischemia.

Pernio or chilblain usually consists of tender or painful, raised, violaceous plaques on the fingers or toes. Occasionally it is found at a more proximal portion of an extremity in a deeper location in the skin or subcutis. Pernio is caused in susceptible individuals by prolonged exposure to cold above the freezing point, especially in damp climates. It is important to distinguish idiopathic chilblains from chilblains in lupus erythematosus or chilblains associated with other autoimmune disease.

In pernio, intense edema of the papillary dermis is observed. A marked perivascular mononuclear cell infiltrate is seen in the upper dermis but sparing the edematous papillary dermis. The blood vessels are said to show a diffuse “fluffy” edema of their walls. The mononuclear infiltrate of the vascular walls is consistent with a lymphocytic vasculitis. The perivascular infiltrate can extend throughout the dermis into the subcutaneous fat. When comparing histology between idiopathic pernio and chilblains associated with autoimmune disease, it has been suggested that perieccrine distribution of lymphocytes is seen more with idiopathic pernio (15).

In pityriasis lichenoides chronica, there is a superficial perivascular and lichenoid infiltrate composed of lymphocytes that extend into the epidermis, where there is vacuolar alteration of the basal layer, mild spongiosis, a few necrotic keratinocytes, and confluent parakeratosis. Melanophages and small numbers of extravasated erythrocytes are commonly seen in the papillary dermis. In PLEVA, there is a perivascular and dense band
like predominantly lymphocytic infiltrate in the papillary dermis that extends into the reticular dermis in a wedge-shaped pattern. The infiltrate obscures the dermal-epidermal junction with pronounced vacuolar alteration of the basal layer, marked exocytosis of lymphocytes and erythrocytes, and intercellular and intracellular edema leading to variable degree of epidermal necrosis. Ultimately, erosion or ulceration may occur. The overlying cornified layer shows parakeratosis and a scaly crust with neutrophils in the more severe cases. Variable degrees of papillary dermal edema, endothelial swelling, and extravasated erythrocytes are seen. Severe vascular damage is rarely found except in a severe febrile ulceronecrotic variant of PLEVA where lymphocytic vasculitis with leukocytoclasis may be seen.

Classic polyarteritis nodosa is a systemic vasculitic disorder in which large arteries are involved and in which ischemic glomerular lesions are
common but glomerulonephritis is rare. Microscopic polyarteritis nodosa, also termed microscopic polyangiitis (MPA) refers to a systemic small-vessel vasculitis primarily affecting arterioles and capillaries that is typically associated with focal necrotizing glomerulonephritis with crescents. The majority of patients with MPA are anti-MPO (p-ANCA) -positive. Some cases of vasculitis present with an overlapping syndrome affecting both small and medium-sized arteries.

The majority of patients with MPA are male and over 50 years of age. Prodromal symptoms include fever, myalgias, arthralgias, and sore throat. The most common clinical feature is renal disease manifesting as microhematuria, proteinuria, or acute oliguric renal failure. Although in classic PAN, cutaneous involvement is rare, 30% to 40% of patients with MPA exhibit skin changes. With cutaneous polyarteritis nodosa, the initial signs include livido reticularis, tender subcutaneous nodules, and ulcerations. Purpura, petechiae, and necrosis can be seen. The legs are most commonly affected (17) With MPA, the most common clinical sign is palpable purpura on the legs. MPA can also present with ulcers, cutaneous necrosis, splinter hemorrhages, and vesicles (18).

The characteristic lesion of classic PAN is a panarteritis involving medium-sized and small arteries. Even though in classic PAN, the arteries show the characteristic changes in many visceral sites, affected skin often shows only small-vessel disease, and arterial involvement is typically focal. The changes affecting cutaneous small vessels are usually those of a necrotizing leukocytoclastic vasculitis (LCV). If there is a clinical presentation of cutaneous nodules, panarteritis similar to visceral lesions is usually detected. In classic PAN, the lesions typically are in different stages of development (i.e., fresh and old). Early lesions show degeneration of the arterial wall with deposition of fibrinoid material, and partial to complete destruction of the external and internal elastic laminae. An infiltrate present within and around the arterial wall is composed largely of neutrophils showing evidence of leukocytoclasia, although it often contains eosinophils. At a later stage, intimal proliferation and thrombosis lead to complete occlusion of the lumen with subsequent ischemia and possibly ulceration. The infiltrate also may contain lymphocytes, histiocytes, and some plasma cells. In the healing stage, there is fibroblastic proliferation extending into the perivascular area. The small vessels of the middle and upper dermis often exhibit a nonspecific lymphocytic perivascular infiltrate.

Many different disease processes can be accompanied by small-vessel vasculitis with predominantly neutrophilic infiltrates. The clinical and histologic manifestations are thus fairly nonspecific. The majority of cases are idiopathic but associated diseases to be considered range from conditions limited to the skin such as most cases of drug-induced vasculitis to systemic conditions such as infections including hepatitis C, malignancies, Henoch-Schönlein purpura, connective tissue diseases, or ANCA-associated disorders such as Churg–Strauss syndrome, microscopic polyangiitis, or Wegener’s granulomatosis (19).

Neutrophilic small-vessel vasculitis is a reaction pattern of small dermal vessels, almost exclusively postcapillary venules, characterized by a combination of vascular damage and an infiltrate composed largely of neutrophils. Because there is often fragmentation of nuclei (karyorrhexis or leukocytoclasis), the term leukocytoclastic vasculitis (LCV) is frequently used. Depending on its severity, this process may be subtle and limited to the superficial dermis or be pandermal and florid and associated with necrosis and ulceration. If edema is prominent, a subepidermal blister may form. If the neutrophilic infiltrate is dense and there is pustule formation, the term pustular vasculitis may be applied. In a typical case of LCV, the dermal vessels show swelling of the endothelial cells and deposits of strongly eosinophilic strands of fibrin within and around their walls. The deposits of fibrin and the marked edema together give the vessel walls a “smudgy” appearance referred to as fibrinoid degeneration. The cellular infiltrate is present predominantly around the dermal blood vessels or within the vascular walls, so that the outline of the blood vessels may appear indistinct. The infiltrate consists mainly of neutrophils and of varying numbers of eosinophils and mononuclear cells. The infiltrate also is scattered throughout the upper dermis in association with fibrin deposits between and within collagen bundles. Extravasation of erythrocytes is commonly present. The appearance of the reaction pattern depends on the stage at which the biopsy is taken. In older lesions, the number of neutrophils may be decreased and the number of mononuclear cells increased so that mononuclear cells may predominate and a designation of a lymphocytic or even granulomatous vasculitis or vascular reaction might be made.

Churg–Strauss syndrome (CSS) is a systemic disease occurring in asthmatic patients
characterized by vasculitis, eosinophilic infiltration of multiple organs, and peripheral eosinophilia. There is considerable overlap of this disease process with other systemic vasculitides, and with other inflammatory disorders exhibiting eosinophils, such as eosinophilic pneumonitis. The internal organs most commonly involved are the lungs, the gastrointestinal tract, and, less commonly, the peripheral nerves and the heart. In contrast to PAN, renal failure is rare. A slightly broader definition of CSS has been proposed requiring asthma, blood hypereosinophilia, and systemic vasculitis involving two or more extrapulmonary organs.

Two types of cutaneous lesions may occur: (1) hemorrhagic lesions similar to Henoch–Schönlein purpura varying from petechiae to extensive ecchymoses, often with areas of erythema and sometimes with necrotic ulcers, and (2) cutaneous–subcutaneous nodules. The extremities are the most common sites of skin lesions, but the trunk may also be involved and some cases are generalized. ANCA tests obtained during an active phase of the disease contain p-ANCA in the majority of cases. There is also a limited form, in which the lesions are confined to the conjunctiva, the skin, and the subcutaneous tissue.

The areas of cutaneous hemorrhage typically show changes of LCV. Eosinophils may be conspicuous. In some instances, the dermis shows a granulomatous reaction composed predominantly of radially arranged histiocytes and, frequently, multinucleated giant cells centered around degenerated collagen fibers. The central portions of the granulomas contain not only degenerated collagen fibers but also dense aggregates of disintegrated cells, particularly eosinophils. These granulomas have been referred to as Churg–Strauss granulomas. However, they are not always present and similar findings can also be observed in other disease processes, such as connective tissue diseases (rheumatoid arthritis and lupus erythematosus), Wegener’s granulomatosis, PAN, lymphoproliferative disorders, subacute bacterial endocarditis, chronic active hepatitis, and inflammatory bowel disease. The granulomas in the subcutaneous tissue may attain considerable size through expansion and confluence, thus giving rise to the clinically apparent cutaneous–subcutaneous nodules. They are embedded in a diffuse inflammatory exudate rich in eosinophils. Similar changes have also been observed in other diseases, such as PAN.

Calciphylaxis is a life-threatening condition in which there is progressive calcification of small and medium-sized vessels of the subcutis with thickening of the intima by fibrosis and subsequent vascular compromise resulting in ischemia and necrosis. It most frequently arises in the setting of hyperparathyroidism associated with chronic renal failure, and is often, but not always, associated with an elevated serum calcium/phosphate product. Clinically, the lesions present as a panniculitis or vasculitis. Bullae, ulcerations, or a livedo reticularis-like eruption can be present. Lesions usually occur over areas with high fat content such as the abdomen, thighs, calves, and buttocks. The digits, breasts, tongue, and penis can also be affected. Early lesions appear as subcutaneous nodules or violaceous plaques. Later lesions with black central necrosis are seen. A biopsy from the center of an eschar will usually show characteristic changes (22).

The histologic changes in calciphylaxis include calcium deposits in the subcutis, chiefly within the walls of small and medium-sized arteries. These deposits can be associated with endovascular fibrosis, thrombosis, or global calcific obliteration. Calcification can also be identified within the soft tissues. The vascular lesions result in ischemic and/or gangrenous necrosis of the subcutaneous fat and overlying skin.

This poorly understood entity is characterized by asymptomatic papules or well-demarcated, slightly infiltrated red plaques, which may develop central clearing. In contrast to the lesions of chronic lupus erythematosus, the surface shows no follicular plugging or atrophy. The eruption may be precipitated or aggravated by sunlight. Lesions arise most often on the face, but may also involve the neck and upper trunk. Affected patients are usually middle-aged men and women. Variable
numbers of lesions (one to many) often persist for several months or several years. They may disappear without sequelae, or recur at previously involved sites or elsewhere. As a historical note, this lesion was one of Lever’s “Five L’s,” which may be slightly modified as: Lymphoma and Leukemia cutis, Lymphocytoma cutis, Jessner’s Lymphocytic infiltrate, Lupus erythematosus, polymorphous Light eruption, and Lepidoptera’the latter intended to signify assault by arthropods of various kinds.

The epidermis may be normal but often appears slightly flattened. In the dermis, there are

moderately dense perivascular and diffuse infiltrates composed of small, mature lymphocytes admixed with occasional histiocytes and plasma cells. The infiltrate may extend around folliculo-sebaceous units and into subcutaneous adipose tissue.

Classic Sweet’s syndrome is characterized by acute onset of fever, leukocytosis, and erythematous plaques, vesicles or pustules infiltrated by neutrophils. This condition typically occurs in middle-aged women after nonspecific infections of the respiratory or gastrointestinal tract. In addition to the classic Sweet’s syndrome, sterile lesions with neutrophilic infiltrates that improve on steroid treatment can be found in a variety of other clinical conditions. Such infiltrates can be associated with inflammatory diseases such as autoimmune disorders or with recovery from infection. They may also develop in patients with hemoproliferative disorders or solid tumors, as well as in pregnant women.

There is a dense perivascular infiltrate composed largely of neutrophils, often with leukocytoclasia. In addition, there are mononuclear cells, such as lymphocytes and histiocytes, and occasional eosinophils. The inflammatory cells typically assume a bandlike
distribution throughout the papillary dermis. The density of the infiltrate varies and may be limited in a small proportion of cases. There is usually vasodilation and swelling of endothelium with moderate erythrocyte extravasation. The prominent edema of the upper dermis in some instances may result in subepidermal blister formation. Extensive vascular damage is not a feature of Sweet’s syndrome. The histologic appearance varies depending on the stage of the process. In later stages, lymphocytes and histiocytes may predominate. It is important to realize that the composition and distribution of the infiltrate are not specific enough to histologically rule out an infectious process.

Neutrophilic dermatosis of the dorsal hands is a recently described entity in the family of neutrophilic dermatoses which also include Sweet’s syndrome, pyoderma gangrenosum, and rheumatoid neutrophilic dermatosis (26,27). These patients present with an eruption that is limited to the dorsal aspect of the hands. The lesions begin as tender plaques and nodules with edema and pustules and a violaceous rim. The pustules may become quite large and some lesions may ulcerate. There is preferential involvement for the radial aspect of the hand. Neutrophilic dermatosis of the dorsal hands most commonly occurs in women (76%) and in adults (mean age of 62 years). There may be an accompanying fever. Unlike classic Sweet’s syndrome, neutrophilic dermatosis of the dorsal hands is generally not associated with an underlying systemic disease or malignancy. However, there have been rare patients with remote history of carcinoma and one with an unclassified type of arthritis.

Biopsies of neutrophilic dermatosis of the dorsal hands reveal a dense neutrophilic infiltrate throughout the dermis which is abscess-like. There may be dermal edema and leukocytoclasia. Some cases have shown vasculitis and fibrinoid necrosis of small vascular channels, however, in many cases, the blood vessels are unaltered (28). This histopathology can be indistinguishable from Sweet’s syndrome and pyoderma gangrenosum making clinical-pathologic correlation paramount. One must always exclude the possibility of an infectious process by the use of special stains for organisms as well as tissue culture. See images on next page.

Erysipelas is an acute superficial cellulitis of the skin caused by group A streptococci. It is characterized by a well-demarcated, slightly indurated, dusky red area with an advancing, palpable border. In some patients, erysipelas has a tendency to recur periodically in the same areas. In the early antibiotic era, the incidence of erysipelas appeared to be on the decline and most cases occurred on the face. More recently, however, there appears to have been an increase in the incidence, and facial sites are now less common whereas erysipelas of the legs is predominant. Obesity has been found to be an independent risk factor for local complications of erysipelas, including hemorrhage, bullous lesions, abscesses, and necrosis (29).

The dermis shows marked edema and dilatation of the lymphatics and capillaries. There is a diffuse infiltrate, composed chiefly of neutrophils, that extends throughout the dermis and occasionally into the subcutaneous fat. It is loosely arranged around dilated blood and lymph vessels. If sections are stained with the Giemsa or Gram stain, streptococci may be found in the tissue and within lymphatics. In cases of recurring erysipelas, the lymph vessels of the dermis and subcutaneous tissue show fibrotic thickening of their walls with partial or complete occlusion of the lumen. Erysipelas and cellulitis must be distinguished from Sweet’s-like eruptions and vice versa. This distinction cannot always be made on histologic grounds alone.

In the usual macular or infiltrative-nodular lesions, there is an extensive cellular infiltrate that is almost invariably separated from the flattened epidermis by a narrow grenz zone of normal collagen. The infiltrate causes destruction of the cutaneous appendages and extends into the subcutaneous fat. In florid early lesions, the macrophages have abundant eosinophilic cytoplasm and contain a mixed population of solid and fragmented bacilli. There is no macrophage activation to form epithelioid cell granulomas. Lymphocyte infiltration is not prominent, but there may be many plasma cells. In time, and with antimycobacterial chemotherapy, degenerate bacilli accumulate in the macrophages constituting the so-called lepra cells or Virchow cells which then have foamy or vacuolated cytoplasm. The Wade-Fite stain reveals that the bacilli are fragmented or granular and, especially in every chronic lesions, disposed in large basophilic clumps called globi. In lepromatous leprosy, in contrast to tuberculoid leprosy, the nerves in the skin may contain considerable numbers of leprosy bacilli, but remain well preserved for a long time and slowly become fibrotic. The histopathology of Lucio (diffuse) leprosy is similar, but with a characteristic heavy bacillation of the small blood vessels in the skin.

The key to diagnosis is identifying the typical Langerhans cell in the appropriate surroundings. The cell has a distinct folded or lobulated, often kidney-shaped nucleus. Nucleoli are not prominent, and the slightly eosinophilic cytoplasm is unremarkable. A typical clinical and light microscopic picture leads to a presumptive diagnosis; confirmation by typical S-100 or peanut agglutinin staining produces a diagnosis; a definite diagnosis requires either a positive CD1a stain or electron microscopic demonstration of Birbeck granules. Although three kinds of histologic reactions have been described in LCH histiocytosis’proliferative, granulomatous, and xanthomatous’only the first two are commonly seen. In general, the proliferative reaction with its almost purely histiocytic infiltrate is typical of acute disseminated LCH and a granulomatous reaction is usually present with chronic focal or multifocal LCH, as the name eosinophilic granuloma suggests. Xanthomatous lesions in the skin are decidedly rare. The proliferative reaction is characterized by the presence of an extensive infiltrate of histiocytes. The infiltrate usually lies close to or involves the epidermis, resulting in ulceration and crusting. Inflammatory cells are also present, most often lymphocytes but also eosinophils. The granulomatous reaction shows extensive aggregates of histiocytes often extending deep into the dermis, with variable eosinophils, multinucleated giant cells, neutrophils, lymphoid cells, and plasma cells may be present.

This rare dermatosis presents as a sudden eruption of a variable number of bright erythematous patches, which over a period of a few days expand into indurated erythematous plaques that may be painful. The overlying epidermis may produce vesicles or small blisters. The disease, if untreated, may persist for a few weeks or months and may be recurrent. Associated or provoking stimuli may include insect bites and cutaneous parasitosis, cutaneous viral infections and drug reactions, leukemic and myeloproliferative disorders, and atopic dermatitis and fungal infections. The patients are usually adults. Peripheral blood eosinophilia is usually present. The clinical appearance may mimic bacterial cellulitis (33).