Jenny O Sobera
Boni E Elewski
Key features
- Cutaneous fungal infections are broadly divided into those that are limited to the stratum corneum, hair and nails, and those that involve the dermis and subcutaneous tissues
- Superficial fungal infections of the skin are due primarily to dermatophytes and Candida spp.
- 'Subcutaneous' mycoses are often the result of implantation, while systemic or 'deep' mycoses of the skin usually represent hematogenous spread or extension from underlying structures
- In the immunocompromised host, opportunistic fungi, e.g. Aspergillus and Mucor, can lead to both cutaneous and systemic infections
This chapter reviews common cutaneous fungal infections, and they are subdivided into three major groups: (1) 'superficial'; (2) 'subcutaneous'; and (3) 'deep' or systemic (see Table 77.1).
SUPERFICIAL MYCOSES
Introduction
The superficial mycoses are due to fungi that only invade fully keratinized tissues, i.e. stratum corneum, hair and nails. They can be further subdivided into those that induce minimal, if any, inflammatory response, e.g. pityriasis (tinea) versicolor, and those that do lead to cutaneous inflammation, e.g. dermatophytoses (Table 77.2). The former are discussed first.
Non-inflammatory superficial mycoses
Synonyms
- Tinea nigra: tinea nigra palmaris et plantaris, superficial phaeohyphomycosis
- Piedra: molestia de Beigel, trichomycosis nodularis
- Pityriasis (tinea) versicolor: tinea versicolor, dermatomycosis furfuracea, tinea flava
Table 77-1. Organization of cutaneous mycoses.
ORGANIZATION OF CUTANEOUS MYCOSES
Superficial / Invade stratum corneum, hair and nails
Subcutaneous / Involve dermis or subcutaneous tissue
Often due to implantation
Systemic / Dermal or subcutaneous involvement
Deep (true pathogens) / Usually reflects hematogenous spread or extension from underlying structures
Opportunistic / Primary or secondary skin lesions in immunocompromised hosts
Table 77-2. Superficial mycoses of the skin.
SUPERFICIAL MYCOSES OF THE SKIN
Cutaneous disorder / Pathogen(s)
Minimal, if any, inflammation / Pityriasis (tinea) versicolor
Tinea nigra
Black piedra
White piedra / Malassezia furfur (Pityrosporum ovale)
Exophiala werneckii
Piedraia hortae
Trichosporon beigelii
Inflammatory response common / Tinea capitis, barbae, faciei, corporis, cruris, manuum, pedis
Cutaneous candidiasis / Trichophyton, Microsporum, Epidermophyton spp.
Candida albicans
History
In 1846, Eichstedt first noted the disease known today as pityriasis (tinea) versicolor. Over the ensuing 150 years, Malassezia furfur, came to be recognized as the causative organism. Recently, however, studies have pointed to M. globosa as the causative agent1. In 1865, Beigel first described piedra after isolating a fungus from a wig. While the fungus he isolated was likely a contaminant, his clinical description is still valid. Tinea nigra was first described several decades later (1890s) by Cerqueira, who named it 'keratomycosis nigricans palmaris'2.
Epidemiology
Tinea nigra and piedra typically occur in tropical climates such as Central and South America, Africa, Asia and, occasionally, in the southeastern US. While any race, age or gender may be infected, the typical patient is a young adult. Additionally, Trichosporon beigelii, the cause of white piedra, is also recognized as an opportunistic pathogen.
The geographic distribution of Malassezia spp. is worldwide. In fact, it is part of the normal flora of human skin (predominantly M. sympodialis). Although pityriasis (tinea) versicolor occurs most frequently in tropical climates with high ambient temperatures and high humidity, it is also a common disorder in temperate climates. No racial or gender difference has been established. The typical patient is a young adult, but people of any age may develop the disease. Interestingly, Malassezia has an oil requirement for growth, accounting for the increased incidence in adolescents and preference for sebum-rich areas of the skin. Malassezia has been implicated in many other skin diseases, including seborrheic dermatitis and atopic dermatitis, but this remains controversial. Neonatal cephalic pustulosis (neonatal acne) is associated with Malassezia spp. in newborn babies, particularly M. sympodialis, according to a recent study3.
Pathogenesis
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Exophiala werneckii and Piedraia hortae are both environmental pathogens. E. werneckii (tinea nigra) can be found in soil and sewage and even in shower stalls under humid conditions. The source of exposure to P. hortae (black piedra) is thought to be the soil. There is no known transmission of these organisms from human to human. T. beigelii (white piedra) is also acquired from the environment; however, it may occasionally be part of the normal flora of the skin and mucous membranes4, particularly the groin and axillary skin.
M. furfur (and other species) normally lives on human skin in amounts so minute as to be undetectable on KOH examination of stratum corneum5. Pityriasis (tinea) versicolor occurs when the round yeast form transforms to the mycelial form. In tropical climates, this change is a result of high temperatures and high humidity. In temperate climates, various factors have been implicated, including oily skin, excessive sweating, immunodeficiency, poor nutrition, pregnancy and corticosteroid use. Because this yeast is lipophilic, use of bath oils and skin lubricants may increase the risk of disease. Risk factors for pityrosporum folliculitis include chronic antibiotic use, immunosuppression and local occlusion.
Clinical features
Piedra Piedra is a superficial infection of the hair shaft. 'Piedra' actually translates as 'stone', and fungal elements adhere to one another to form nodules, or 'stones', along the hair shaft. There are two major forms - black piedra and white piedra - and they are distinguished by clinical appearance plus microscopic examination (Table 77.3). Patients with black piedra typically present with asymptomatic brown to black nodules along the hair shaft. Infection usually commences under the cuticle of the hair shaft and extends outward. Hair breakage may occur as a result of shaft rupture at the site of the nodules. As the nodules enlarge they can even envelope the hair shaft (Fig. 77.1).
In white piedra, the infection also begins beneath the cuticle and grows through the hair shaft, causing weakening and breaking of the hair. The soft, less adherent nodules of white piedra are generally white but may also be red, green or light brown in color. The incidence of white piedra in the pubic region has increased since the start of the HIV epidemic. In immunosuppressed patients, T. beigelii can cause trichosporosis, a serious systemic infection with fungemia, fever, pulmonary infiltrates, skin lesions (papulovesicular and purpuric, often with central necrosis) and renal disease4.
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Figure 77.1 Causes of nodules on hair shafts.
Table 77-3. Comparison of black and white piedra6.
COMPARISON OF BLACK AND WHITE PIEDRA4
White piedra / Black piedra
Nodule color / White (may be red, green or light brown) / Brown to black
Nodule firmness / Soft / Hard
Nodule adherence to the hair shaft / Loose / Firm
Typical location / Face and axillae (occasionally in pubic region) / Scalp and face (occasionally in pubic region)
Climate / Tropical / Temperate
Causative organism / Trichosporon beigelii / Piedraia hortae
KOH / Non-dematiaceous hyphae with blastoconidia and arthroconidia / Dematiaceous hyphae with asci and ascospores*
Culture / Moist, creme-colored, yeast-like colonies / Slow-growing, dark brown to black colonies
Treatment / Clip affected hairs, wash affected hairs with antifungal shampoo / Clip affected hairs, wash affected hairs with antifungal shampoo
* Sexual reproduction.
Tinea nigra After a 10- to 15-day incubation period, tinea nigra most commonly presents as a single, sharply marginated, brown to gray to green macule or patch that can be velvety or have mild scale. There are usually no associated symptoms (i.e. pruritus), and no predispositions have been identified. While most frequently seen on the palms, tinea nigra can also appear on the soles, neck and trunk. Although palmoplantar lesions are said to resemble acquired acral melanocytic nevi, the former are usually larger, lighter in color and lack the linear striations of the latter. Tinea nigra can also have darker pigmentation of the advancing border as compared to the center. While the disease tends to be chronic, recurrence after effective treatment is infrequent except in the case of re-exposure.
Pityriasis (tinea) versicolor Patients usually present with multiple oval to round patches or thin plaques with mild scale. Demonstration of this associated scale may require scratching of its surface. Centrally, within the areas of involvement, the lesions are often confluent and they may be quite extensive. Seborrheic areas, in particular the upper trunk and shoulders, are the favored sites of involvement. Less frequently, lesions are seen on the face (more so in children), scalp, antecubital fossae and groin. When pityriasis (tinea) versicolor involves flexural areas, it is sometimes referred to as 'inverse' pityriasis (tinea) versicolor.
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Figure 77.2 Pityriasis (tinea) versicolor, hyperpigmented variant. Courtesy of Kalman Watsky, M.D.
The most common colors are tan (hypopigmentation; see Chapter 66) and brown (hyperpigmentation; Fig. 77.2); occasionally there is associated inflammation with a pink color. Decreased pigmentation may be secondary to the inhibitory effects of dicarboxylic acids on melanocytes (the latter result from metabolism of surface lipids by the yeast) or decreased tanning, due to the ability of the fungus to filter sunlight. In general, pityriasis (tinea) versicolor is asymptomatic and the major concern is its appearance.
Pityrosporum folliculitis This condition is most commonly seen in young women and is characterized by pruritic follicular papules and pustules on the trunk, arms, neck and, occasionally, the face. It is due to excessive growth of P. orbiculare (a culturally identical variant of M. furfur) within the hair follicle with resulting inflammation (from yeast products and free fatty acids produced from fungal lipase). Only yeast forms are observed, i.e. no hyphal forms as in pityriasis (tinea) versicolor. Several Malassezia species have also been implicated in neonatal cephalic pustulosis ('neonatal acne'; Chapter 36).
Pathology and fungal culture
For both black and white piedra, cut hair shafts are placed in KOH and a 'crush preparation' is examined microscopically. In a black piedra nodule, dematiaceous hyphae are seen around an organized cluster of asci, each of which contains eight ascospores. The ascospores represent the sexual phase of P. hortae. P. hortae grows very slowly when cultured and yields a green to black colony with velvety texture (asexual phase)7.
KOH preparation of a crushed white piedra nodule reveals nondematiaceous hyphae, blastoconidia and arthroconidia, representing the asexual state. When cultured, T. beigelii grows rapidly forming moist, cream-colored, yeast-like colonies that some have likened to butter cream frosting. On Mycosel® agar, the organism will be inhibited by the presence of cycloheximide. T. beigelii is often isolated from skin and nail specimens, and the significance of this must be correlated with clinical findings.
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Figure 77.3 Potassium hydroxide preparations. A Superficial skin scrapings from pityriasis (tinea) versicolor demonstrating yeast and short mycelial forms. B A dermatophyte, in this case T. tonsurans, demonstrating branching hyphae. A, Courtesy of Ron Rapini, M.D.
Biopsies of pityriasis (tinea) versicolor and tinea nigra are usually not performed as the KOH examination of associated scale is usually diagnostic. In the former, both hyphal and yeast forms are seen; although likened to 'spaghetti and meatballs', the findings more resemble 'ziti and meatballs' (Fig. 77.3A). In the latter, KOH examination reveals septate pigmented hyphae. When biopsy specimens are obtained, similar findings are observed within the stratum corneum. In KOH examination of expressed follicular contents or biopsy specimens of Pityrosporum folliculitis, only yeast forms are seen. Cultures of E. werneckii first appear as pasty, green-black colonies with a yeast-like appearance. However, after about two weeks the appearance changes to that of a fuzzy, dematiaceous (dark in color) mold. Culture of Malassezia is generally not indicated, but if necessary, the plate must be overlaid with sterile oil because of its lipophilic nature.
Differential diagnosis
Piedra is generally diagnosed by clinical and microscopic inspection of a hair shaft and must be distinguished from pediculosis (nits), hair casts, trichorrhexis nodosa, trichomycosis axillaris (see Chapter 74 and Fig. 77.1) and the scales of psoriasis and eczema. Unlike eczema and psoriasis, the scalp will typically appear normal in piedra.
In most patients the diagnosis of tinea nigra is made clinically and confirmed via KOH examination and/or fungal culture. Its distinction from acral melanocytic nevi has been discussed previously (see above); occasionally, tinea nigra could be confused with a fixed drug eruption, post-inflammatory hyperpigmentation, or staining from chemicals, pigments and dyes. Cutaneous melanoma has even been misdiagnosed as tinea nigra, with unfortunate results.
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Clinical examination often leads to the correct diagnosis of pityriasis (tinea) versicolor; however, vitiligo, pityriasis alba and other forms of postinflammatory hypopigmentation (see Chapter 66), seborrheic dermatitis, pityriasis rosea and secondary syphilis may mimic the disease. Wood's light examination (revealing bright yellow fluorescence) and then direct microscopy establish the diagnosis. Pityrosporum folliculitis must be differentiated from other causes of folliculitis (see Chapter 40, Table 40.1), in particular itching folliculitis, as well as acne vulgaris.
Treatment
Clipping hairs with adherent nodules as well as shampooing the affected hairs with 2% ketoconazole shampoo is usually effective treatment for piedra (Table 77.3). Oral terbinafine is possibly of some therapeutic benefit. For treatment of tinea nigra, topical keratolytic agents such as Whitfield's ointment (typically 6% benzoic acid plus 3% salicylic acid8) are effective, as are topical antifungal medications, e.g. the azole and allylamine families. Several weeks of therapy may be required to prevent recurrence of disease. Systemic therapy is generally not indicated, and griseofulvin is not effective.
Patients with pityriasis (tinea) versicolor usually respond to topical antimycotic treatments. We instruct the patient to treat all the skin from the neck down to the knees, even if only a small area is clinically involved. Ketoconazole (1 or 2%) or 2.5% selenium sulfide shampoo is quite effective. Treatment is twice weekly for two to four weeks, the preparation is left on the skin for 10-15 minutes before it is removed. Other topical alternatives include azole/allylamine creams and lotions, 50% propylene glycol in water (cosmetically pleasing), nystatin, salicylic acid and a variety of over-the-counter dandruff shampoos. Post-inflammatory pigmentary changes may respond to low potency topical corticosteroids but usually require tincture of time.
Systemic therapy with ketoconazole, fluconazole or itraconazole (see Chapter 128) may provide simple and effective treatment for pityriasis (tinea) versicolor. A regimen of short duration (3 to 7 days) is usually successful. The rate of recurrence of pityriasis (tinea) versicolor is very high, especially in hot humid climates. Patients at high risk for recurrence may be helped by using ketoconazole shampoo once weekly as 'soap'. Another preventative measure is once monthly dosing of oral ketoconazole, fluconazole or itraconazole. Blood monitoring may be required, however, especially in the case of ketoconazole.