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DERMATOPHYTOSIS. In tinea capitis and tinea barbae , infection of follicles usually starts with colonization of the stratum corneum of the perifollicular epidermis.
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In tineacapitis and tineabarbae, infection of follicles usually starts with colonization of the stratum corneum of the perifollicularepidermis. • Endothrix infections are caused by T. tonsuransor T. violaceum. Except for T. schoenleinii,which causes favus, dermatophytes infecting hair shafts cause ectothrix infections. • The dermis, which rarely contains fungi, shows a perifollicular mononuclear cell infiltrate of varying intensity. • In kerionCelsi, there is a pronounced inflammatory tissue reaction to the fungi with follicular pustule formation and interfollicularneutrophilic infiltration as well as a marked chronic inflammatory infiltrate surrounding the hair follicles. • In tinea of the glabrous skin, which includes tineafaciei,tineacorporis, tineacruris, and tinea of the feet and hands,fungi occur only in the horny layers of the epidermis and do not invade hairs and hair follicles. Two exceptions to this are T.rubrum and T. verrucosum, both of which may invade hairs and hair follicles, causing a subsequent perifolliculitis.
In infections with Microsporum or Trichophyton, only hyphae are seen, and in infections with E. floccosum chains of spores are present. If fungi are present in the horny layer, they usually are "sandwiched" between two zones of cornified cells, the upper being orthokeratoticand the lower consisting partially of parakeratotic cells. • The presence of neutrophils in the stratum corneum is another valuable diagnosticclue. • Depending on the degree of reaction of the skin to the presence of fungi, the histologic features of an acute, subacute, or chronic spongiotic dermatitis can be seen. • On staining with the PAS reaction or GMS, nodular perifolliculitis, or Majocchi's granuloma, caused by T rubrumshows numerous hyphae and spores within hairs and hair follicles and in the inflammatory infiltrate of the dermis.
Microscopic examination of potassium hydroxide mounts or cultures of nail fragments often establish a diagnosis of onychomycosis. • By far, T rubrum is the most common causal fungus; occasionally, T mentagrophytes is present. • Three histologic patterns are common in nail plate biopsies of onychomycosis. In superficial infections, mycelial elements, best visualized with PAS or GMS, are seen in the outer layer of the nail plate. • The second histologic pattern is seen in clinical onycholysis when PAS stained sections of nail plate reveal slender, uniform mycelial elements invading the undersurface of the nail plate. • The third common histologic pattern is seen in Candida infections, where hyphal forms are seen on the undersurface of the nail plate.
In contrast to other fungal infections of the glabrous skin, the horny layer in lesions of pityriasis (tinea) versicolor contains abundant fungi. • Malassezia (Pityrosporum) is present as a combination of both hyphae and spores, the light microscopic appearance of which is often referred to as spaghetti and meatballs. • The inflammatory response in pityriasisversicolor is usually minimal, although there may occasionally be slight hyperkeratosis and spongiosis, or a minimal superficial perivascular lymphocytic infiltrate.
The involved pilosebaceousfollicles show hyperkeratosis with dilatation resulting from plugging of the infundibulum with keratinous material. Inflammatory cells are present both within and around the follicular infundibulum. • PAS stained sections show PAS positive, diastase-resistant, spheric to oval, singly budding yeast organisms that are 2 to 4 micro m in diameter.
CANDIDIASIS Acute Mucocutaneous Candidiasis
Cutaneous and mucous membrane candida infection show similar features. • If the primary lesion is a vesicle or pustule, it is usually subcorneal as in impetigo. • In some instances, the pustules have a spongiform appearance ,similar to the spongiform pustules of Kogoj seen in pustular psoriasis. • Pseudohyphaeand ovoid spores, with some of the latter in the budding stage. • These septatepseudohyphae show branching at a 90-degree angle and measure from 2 to 4 micro m diameter.
CANDIDIASIS Chronic Mucocutaneous Candidiasis
The histologic findings are identical with those of acute mucocutaneous candidiasis, except in cases of candidal granuloma. • Candidal granulomashows pronounced epidermal papillomatosis and hyperkeratosis and a dense infiltrate in the dermis composed of lymphoid cells, neutrophils, plasma cells, and multinucleated giant cells. The infiltrate may extend into the subcutis. • C. albicansusually is present only in the stratum corneum.
Histologic examination reveals one or several aggregates of hyphae and spores focally within the dermis, often at sites of vascular damage and generally visible only in sections stained with the PAS reaction or GMS. • The aggregates of hyphae and spores may lie in an area of leukocytoclastic vasculitis, within a microabscess, or in an area of only mild inflammation. • The epidermis is usually unaffected. • Candida commonly causes onycholysis but distinguishes itself histologically from the dermatophytes by its lack of nail plate invasion. • Yeast forms may be seen along the undersurface of the nail plate. • Candida may mimic the psoriasiform changes and inflammatory response of onychomycosis caused by dermatophytes.
Unlike the case with most deep cutaneous fungal infections, pseudoepitheliomatous epidermal hyperplasia is not characteristic of cutaneous aspergillosis. • Numerous Aspergillushyphae are seen in the dermis. • Hyphae may be seen in H&E-stained sections, but PAS or silvermethenamine staining may be required. • Spores are absent.
The histologic changes in zygomycosis are primarily dermal. • The hallmark of zygomycosis is vascular invasionby very large, long, nonseptate hyphae with thrombosis and infarction. • Hyphae branch at 90-degree angles and may also be found in the surrounding tissue. • Spores are rarely seen.
Lesions of subcutaneous phaeohyphomycosis start as small, often stellate foci of suppurativegranulomatous inflammation. • The area of inflammation gradually enlarges and usually forms a single large cavity with a surrounding fibrous capsule, the so-called phaeohyphomycotic cyst. • The central space is filled with pus formed of polymorphonuclear leukocytes and fibrin. • Mycelia, if present, are more loosely arranged than the compact masses of hyphae seen in eumycetoma.
Although fungi are found mainly in the deeper layers of the dermis and in the subcutaneous region in the hematogenous and the traumatogenic forms, they are localized predominantly in the epidermis in cases in which Alternaria colonizes preexisting lesions. • The dermis shows a suppurative granulomatous reaction associated with variable pseudoepitheliomatous epidermal hyperplasia and ulceration. • The hyphae and spores stain deeply with PAS or silver methenamine.
Early lesions of blastomycosis demonstrate a dermal inflammatory infiltrate of polymorphonuclear leukocytes with numerous organisms. • Later, a verrucous histologic pattern with pseudoepitheliomatous hyperplasia is characteristic. • There is considerable downward proliferation of the epidermis, often amounting to pseudocarcinomatous hyperplasia. Intraepidermal abscesses often are present. • Occasionally, there are tuberculoid formations, although without evidence of caseation necrosis.
Examination of cutaneous or mucosal lesions reveals a granulomatous infiltrate showing epithelioid and giant cells in association with an acute inflammatory infiltrate and abscess formation. • Spores are best demonstrated with the PAS reaction or methenaminesilver. • Pseudoepitheliomatous hyperplasia may be marked.
The dermis shows an extensive infiltrate of macrophages and large giant cells separated from a usually atrophic epidermis by a grenz zone. • Numerous fungus spores lie both within these cells and outside of them. • They possess a thick capsule, about 1 micr m in thickness, with a tip that gives the organisms a distinctive "lemon-like" appearance.
Cutaneous chromomycosisresembles North American blastomycosis in that both demonstrate a lichenoid granulomatous inflammatory pattern. • In chromomycosis, there is pseudoepitheliomatous epidermal hyperplasia and an extensive dermal infiltrate composed of many epithelioid histiocytes. • Tuberculoid formations may be present, but caseation necrosis is absent. • Transepidermal elimination of fungal spores may be observed, resulting in clinically visible black dots.
In primary cutaneous inoculation coccidioidomycosis, a dense dermal inflammatory infiltrate of neutrophils, eosinophils, lymphoid cells, and plasma cells with an occasional giant cell can be observed. • The verrucous nodules and plaques of the skin in systemic coccidioidomycosis histologically resemble those of North American blastomycosis. • The nodose skin lesions occurring in primary pulmonary coccidioidomycosishave the same histologic appearance as those in idiopathic erythema nodosum.
Two types of histologic reaction to infection with C. neoftrmans may occur in the skin as well as elsewhere: gelatinous and granulomatous. • Gelatinous lesions show numerous organisms in aggregates and only very little tissue reaction. • In contrast, granulomatous lesions show a pronounced tissue reaction consisting of histiocytes, giant cells, lymphoid cells, and fibroblasts. • Cryptococcal cellulitis shows nonspecific acute and chronic inflammation in which cryptococcal organisms can be demonstrated with the PAS and mucicarmine stains.
The diagnostic featurein all types of cutaneous histoplasmosis is the presence of tiny 2 to 4 micro m sporeswithin the cytoplasm of macrophages and variably within giant cells. • In acute disseminated histoplasmosis, lesions consist mostly of heavily parasitized histiocyteswith relatively little surrounding tissue reaction. • Cutaneous lesions in the chronic form of the disease tend to be composed of better-differentiated macrophages with fewer organisms. • A suppurative granulomatous pattern may develop, especially in ulcerated lesions. • African Histoplasmosis: The cutaneous lesions show a dense, mixed cellular infiltrate containing numerous giant cells and scatteredhistiocytes, lymphocytes, and plasma cells. There are focal aggregates of neutrophils forming small abscesses.
Early primary cutaneous lesionsshow a nonspecific inflammatory infiltrate composed of neutrophils, lymphoid cells, plasma cells, and histiocytes. Longer-standing, clinically verrucous lesionsshow a hyperplastic epidermis with small, intraepidermal, and dermal lymphoplasmacyticinfiltrate with small abscesses, eosinophils, giant cells, and small granulomas often associated with asteroid bodies. • A characteristic arrangement of the infiltrate in three zones may develop. These include a central "suppurative" zone composed of neutrophils; surrounding it, a "tuberculoid" zone with epithelioid cells and multinucleated histiocytes; and peripheral to it, a "round cell" zone of lymphoid cells and plasma cells.
Histologic examination of the indurated skin shows extensive granulation tissue containing abscesses that may lead into sinuses. • In the early phase of the disease, the tissue surrounding the abscesses is composed of lymphoid cells, plasma cells, histiocyres,and fibroblasts, whereas in the late phase, fibroblasts may predominate. • The diagnosis can be established only by finding' the "sulfur granules“. • A Gram stain aids in differentiating bacterial from fungal causes of mycetoma; the filaments of actinomycetoma are gram positive, whereas the hyphae in grains of eumycetoma are gram negative.
The epithelium is hyperplastic with papillomatosis and deep invaginations, some of which form pseudocysts. • Numerous globular cysts of varying shape, representing sporangia in different stages of development, give the corium a distinctive "Swiss cheese" appearance. There is a surrounding dense, mixed inflammatory infiltrate with lymphocytes and histiocytes, including occasional giant cells,plasma cells, neutrophils, and eosinophils.
The histologic appearance, like the clinical appearance, is notcharacteristic. • There is a mixed inflammatory infiltrate with areas of necrosis and fairly numerous giant cells.
