Dermatophytosis And Other Sup... Health Article

The main zoophilic dermatophyte fungi are shown in Table 265-1. Each organism is primarily an animal pathogen that sometimes causes human infection. In each case there is usually a range of host specificities, from organisms such as Microsporum nanum, whose natural host is the pig and which does not infect other animals, to Trichophyton mentagrophytes, which affects a range of different rodent species as well as cats, dogs, and horses.

The host preferences of T. mentagrophytes coupled with small clinical and cultural differences have led many mycologists to subdivide this group into different species or subspecies (the mentagrophytes complex). Under this classification T. mentagrophytes quinckeanum ( Trichophyton quinckeanum ) is used to describe the fungus that causes the clinical pattern of favus in mice, an infection associated with the formation of epithelial crusts. In most temperate countries Trichophyton verrucosum, the cause of cattle ringworm, and Microsporum canis, a dermatophyte that causes infections in cats or dogs, are the most common zoophilic dermatophytes that cause human infections.

Of all the zoophilic dermatophytes, M. canis is probably the most prevalent throughout the world. Its appearance in the tropics is a comparatively recent event, and it is mainly found there as a cause of disease in urban communities. ⁷ Occasionally, the distribution of zoophilic dermatophytes may appear to be difficult to explain, but usually it reflects the distribution of the animal host. For instance, Trichophyton erinacei ( T. mentagrophytes ) is mainly confined to Europe and New Zealand. It is carried by hedgehogs, which were introduced into New Zealand in the 19th century from England. Microsporum persicolor is a rare cause of human infections in Europe, where it has been isolated from the bank vole, whose distribution is similarly restricted. Trichophyton simii is associated with monkeys in India and the Far East, and human infections are seen only in these areas. ⁸

Dermatophytes originating from soil, such as Microsporum gypseum, are infrequent causes of human disease, although they may be seen more commonly in certain parts of the tropics such as the western Pacific and Central America. In other areas they usually cause sporadic infections, although occasionally they may be responsible for outbreaks of human disease in appropriately exposed occupational groups such as gardeners or farm workers. ⁸

Dermatophytes that are natural pathogens of humans are the most common cause of human dermatophytosis. They include organisms that mainly cause infections of glabrous skin of the feet or hands as well as a range of pathogens whose invasion may involve penetration of the hair shaft. The most common of these organisms in most parts of the world is T. rubrum, which causes tinea pedis or tinea cruris in temperate climates and, particularly in the tropics, tinea corporis. Cases of infection that are due to T. rubrum were once rare in the Western Hemisphere, but the infection has spread rapidly during the past 40 years. The ability of this dermatophyte to cause noninflammatory chronic infections of the feet, among other sites, that are easily transmitted is probably an important factor that has determined its spread in recent years. ⁷ The large population movements during World War II are also thought to have contributed to the spread of the disease. Despite this, a variant with distinct morphologic appearances may be isolated from patients with tinea corporis in remote rural areas of the New World and Old World tropics, which suggests that, although endemic disease caused by this species has been present for a considerable time, the key adaptation leading to spread was the appearance of strains capable of causing indolent and noninflammatory infections of peripheral skin sites. ⁹

Spread of the organisms that infect glabrous skin is largely through contact with infected desquamated skin scales. Classically, this occurs in bathing areas or shower rooms where large numbers of individuals share common facilities, for instance, in military camps or factories. ¹⁰ In the U.K. coal mining industry as many as 30 to 35 of coal miners had dermatophyte infections affecting their feet. In most cases this was due to T. rubrum, although Trichophyton interdigitale (mentagrophytes) may also be isolated. ¹¹ Changing rooms in other heavy industrial companies, the police and armed forces, schools, and public swimming pools are also sites for infection. By contrast, transmission within the home as a reflection of conjugal or familial cases is not common, ¹² although it has been suggested that some patients show genetic susceptibility. E. floccosum may also cause foot infections, although it is particularly associated with tinea cruris either as a sporadic disease or in institutions such as prisons or military barracks. These infections are not geographically restricted, even though there are variations in different countries. In many tropical areas, particularly the Far East, T. mentagrophytes is less commonly a cause of interdigital foot disease, and patients are infected by the zoophilic variety of this species on sites other than the feet. ¹³

Tinea corporis (tinea imbricata), caused by the anthropophilic dermatophyte T. concentricum, has an unusual distribution confined to remote parts of the humid tropics. ¹⁴ The main endemic areas are the western Pacific, Malaysia, Assam, and parts of the Amazon basin in Brazil. Infants may be affected shortly after birth, and spontaneous recovery is unusual. Large numbers of viable organisms can be cultured from the houses of infected families. Visitors to endemic areas are rarely infected. Cases have also been described in southern Mexico, where the disease appears to fluctuate in severity with the season.

The distribution of some of the other anthropophilic dermatophytes that cause tinea capitis in children as well as other clinical forms of disease such as tinea corporis or onychomycosis may be more restricted. The reasons for this are not entirely clear unless the prevalence of these infections in children, who form a relatively stable population with little opportunity for travel, limits the spread of the disease to certain localities. Whatever the reason, these scalp infections are often found in defined endemic areas (Table 265-2). The situation is best illustrated by the distribution of Trichophyton spp. causing tinea capitis in West Africa, where the endemic areas for Trichophyton soudanense, Trichophyton yaoundei, and Trichophyton gourvilii are distinct, although there is some overlap. ¹⁵ Trichophyton tonsurans in the United Kingdom, United States, and Mexico and Trichophyton violaceum in India, East Africa, and the Middle East are the predominant causes of scalp infection in some areas. The situation does not always remain stable, and the slow increase in numbers of T. tonsurans in the United States was followed by spread to the United Kingdom and some parts of Europe. ⁷ Endemic anthropophilic scalp infections that are due to Microsporum spp. are less common. For instance, Microsporum ferrugineum is found occasionally in the Far East or central Europe. Microsporum rivalieri is seen in Africa, Democratic Republic of Congo, and Angola. The most widely distributed of this genus is Microsporum audouinii. Once common throughout Europe, it is now rare in this area, but it is still an important cause of tinea capitis in West Africa and in parts of the United States and Latin America. Microsporum canis has begun to spread in Eastern Europe in the past few years.

The infection caused by T. schoenleinii, favus, has characteristic clinical features. It was once common in Europe but has now largely disappeared from many areas, although there are still pockets of infection in parts of the United States, South America, South Africa (Botswana), and North Africa. One of the features of this disease is the development of crusts or scutula on the scalp. Hairs are invaded, but shedding is delayed because they are not structurally damaged until late in the course of the infection. Although tinea capitis is normally a disease of children, adult women with favus are occasionally seen.

Dermatophytes causing scalp disease may be carried on the skin surface without invading the skin or hair. A small proportion of carriers develop infections within 6 months, others lose the fungus, and the rest remain carriers. ¹⁶ It is likely, though, that some carriers are simply patients with limited but undetected infections. The same can also be seen in foot infections, where carriage can also occur.

Tinea pedis is usually caused by infection with either T. rubrum or T. mentagrophytes (interdigitale), less commonly by E. floccosum. The infection usually starts in the lateral interdigital spaces of the foot or on the undersurface of the lateral aspects of the toes. The main symptom is itching, although this is variable. The skin usually cracks and may become severely macerated. In some cases, often where T. mentagrophytes is the causative organism, bullae are formed, and there is severe itching. The infection may also spread onto the dorsum of the feet, usually on the lateral side of the foot. Involvement of the sole is common in T. rubrum infections, and part of or the entire sole becomes erythematous and covered with dry scales. This is most noticeable along the lateral borders of the sole, where the appearance often leads to the term moccasin or dry-type infection. Blisters may also be formed in small clusters on the sole. The course of infection is variable. In noninflammatory forms the interdigital scaling is often chronic or intermittent, whereas if blisters are formed, the infection usually resolves but may recur several months later. The main complications of tinea pedis are bacterial cellulitis and fungal invasion of the toenails (onychomycosis) or the skin of the dorsum of the foot and leg.

Tinea pedis is usually seen in young adults or teenage children. It is particularly common in institutions or places where common bathing facilities are used. The clinical manifestations of infection are altered in patients with T-lymphocyte abnormalities, including those with acquired immunodeficiency syndrome (AIDS), in whom there is often extensive spread of the lesions onto the dorsal surface of the foot.

Scaling between the toes is often referred to as athletes foot, but similar clinical signs may be produced by a variety of organisms. Erythrasma that is due to Corynebacterium minutissimum may present with scaling and, in particular, maceration between the toe webs. Gram-negative bacteria such as Pseudomonas and Proteus spp. may contribute to interdigital disease in patients with closely apposed web spaces or whose work involves immersion in water. These organisms may replace the original dermatophytes in this site, an infection known as dermatophytosis complex. ²⁵ Staphylococcus aureus may cause secondary infections of foot, but characteristically this starts on the dorsum of the foot over the first two digits. The mold fungi Scytalidium dimidiatum and S. hyalinum may cause interdigital scaling as well as nail disease and sole involvement that is indistinguishable from dry-type infections caused by dermatophytes.

The most common dermatophytes associated with groin infections are T. rubrum and E. floccosum. This infection is also called jock itch. The infection starts with scaling and irritation in the groin. The rash usually involves the anterior aspect of the thighs, less commonly the scrotum. The leading edge extending onto the thighs is prominent and may contain follicular papules and pustules. The infection may also spread to the anal cleft. Although tinea cruris is mainly a disease of young adult men, it may affect women, particularly in the tropics, where the infection is often less well delineated and spreads in a band around the waist area.

Tinea cruris, as with tinea pedis, there may be clustering of cases in institutionalized groups such as in military camps. The toe webs are also often infected in patients with tinea cruris.

Erythrasma of the groin may also cause a localized rash with itching. However, here the leading edge is less prominent than in tinea cruris, and the rash is covered with fine wrinkles. Erythrasma fluoresces pink under Woods light. Candidiasis of the groin may also mimic tinea cruris, but an important clue to the presence of Candida is the appearance of small satellite pustules beyond the free margin of the rash. Flexural psoriasis causes a vivid red and uniformly scaling rash in the groin, and there is usually at least one other site with typical psoriatic plaques.

Tinea corporis, or ringworm, is one of the most commonly misdiagnosed skin diseases. Cases of this infection are not common in temperate climates, although it is seen more frequently in the tropics. Generally there are various clinical presentations of this form of dermatophytosis. Most lesions have a prominent edge that may contain pustules or follicular papules, and the center of the lesion is often less inflamed and scaly (Fig. 265-1). Sites commonly involved are the trunk and legs. Itching is variable, and lesions may be single or multiple. Generally, infections caused by anthropophilic dermatophytes such as T. rubrum are less inflammatory and less clearly demarcated, and in some patients it is necessary to search for the margin carefully to delineate the rash. Lesions are usually hyperpigmented in pigmented skins. By contrast, zoophilic infections such as those caused by M. canis and T. verrucosum are more inflammatory, and lesions may become elevated and contain pustules. Infections caused by M. gypseum are also usually inflammatory and may have a brick-red appearance.

These clinical patterns vary with the site of infection. T. rubrum infections on the lower parts of the legs may lead to the formation of single or multiple deep nodules that may mimic erythema nodosum. ²⁶ The overlying skin is dry, red, and scaly, which is a useful clue to the correct diagnosis. This form of infection, which is known as nodular folliculitis, follows follicular penetration of the hair follicles of the lower portions of the legs by the fungus. It is seen mainly in women. In patients with defective T-lymphocyte function, scaling is often minimal, and the rash of tinea corporis consists of grouped papules or pustules without significant erythema.

Tinea corporis can occur at any age, although in temperate countries it is most often seen in children and is associated with zoophilic infections.

A number of different conditions should be considered in the differential diagnosis of tinea corporis, ranging from eczema to psoriasis or annular erythema. The important points to look for are the annular scaling margin of lesions and follicular prominence, which are features of dermatophytosis. However, it may be necessary to take scrapings for laboratory culture where there is doubt.

Tinea imbricata is a variant of tinea corporis that is caused by T. concentricum. The geographic distribution of the disease is shown in Table 265-2. Patients may be infected at any age, although infants and young children are frequently affected. The main characteristic of the rash is the formation of concentric rings of scales (Fig. 265-2) over large parts of the body that amalgamate to form waves of scaling. ¹⁴ There are other clinical varieties of tinea imbricata, including the diffuse scaling variety, in which large flakes of skin are prominent. The disease gets its name imbricata (Latin, tiled) from this clinical pattern. Other patients may have itchy lichenified lesions on the forearms. The face may be affected, as well as the sides of the fingers, but the feet, scalp, axillae, and groin are usually spared. Tinea imbricata is seldom mistaken for other diseases, and the inhabitants of endemic areas easily recognize the appearance of the infection and have specific names for it. In Papua New Guinea, it is called sipoma or grille.

The term tinea manuum is used for dermatophyte infections involving the hand. In some patients the dorsum of the hand may be affected, but most commonly the disease occurs on the palmar surface. It is a characteristic of dry-type infections at this site to find that only one palm is involved, although in some patients both may be infected. The clinical features are identical to those seen with dry-type infections of the sole. The usual cause is T. rubrum, and the feet are often involved in addition to the hands.

Dermatophytosis affecting the palm may be confused with eczema, but the unilateral distribution of the infection and the common accompanying findings of onychomycosis and tinea pedis are helpful clues. Patients with palmoplantar keratoderma (tylosis) are particularly susceptible to superinfection of the palms and soles with dermatophytes. ²⁷ This complication may be difficult to identify, but the skin may blister and the hand usually itches. In these patients fungi other than T. rubrum may be implicated.

Dermatophyte infections of the face are usually caused by the same organisms associated with tinea corporis. Infections that are due to T. rubrum at this site are often particularly difficult to recognize (tinea incognito). The facial skin becomes itchy and red, but the margin of the rash may be difficult to discern (Fig. 265-3). Some patients report that the facial rash is exacerbated by sun exposure. In other instances lesions are more readily noticeable and affect the ears. Tinea faciei has been reported more frequently in AIDS patients.

Tinea barbae, infection of the neck and beard area, may be pustular and inflamed because it is often caused by zoophilic organisms such as T. verrucosum. It is more localized than sycosis barbae caused by S. aureus, a helpful point in distinguishing the two conditions.

Scalp ringworm, or tinea capitis, is a disease of childhood. Its prevalence varies considerably in different parts of the world. The disease is widespread in some urban areas in the United States, Africa, and Europe. Tinea capitis is also common in parts of India. In northern Europe the disease is sporadic. The main reasons for these differences in the prevalence of infection in different localities are the nature of the infecting organisms and the availability of control measures. Endemic infections affecting large numbers of children are associated with anthropophilic organisms, and sporadic disease with zoophilic fungi. Tinea capitis is usually classified by the pattern of hair shaft invasion. Dermatophyte infections in which arthrospores are formed on the outside of the hair shaft are known as ectothrix infections and those in which the spores develop within the hair itself as endothrix infections. In T. schoenleinii infections the fungi invade the hair medulla but then regress and leave tunnels containing air within the hair shaft (the favic pattern). Although it is identified as a childhood disease, adults exposed to T. tonsurans infections and patients with AIDS may develop tinea capitis.

The main clinical feature of dermatophyte scalp infections are the appearance of scaling of the scalp skin that is associated with a variable degree of erythema and inflammation and alopecia. In some cases the infection closely resembles seborrheic dermatitis or dandruff of the scalp. The infection is often accompanied by itching. A pathognomonic feature is hair loss. In ectothrix infections hairs often break a few millimeters or more above the skin surface (Fig. 265-4). Broken or infected hairs are also slightly swollen and have a dull appearance. In endothrix infections, parasitized hairs break at the skin level. In some endothrix infections scattered stumps can be seen within areas of hair loss (black-dot ringworm). In such cases inflammation may be minimal. A further element in tinea capitis is the variable amount of inflammation, but in some cases the whole area becomes pustular and covered with a thick scale or exudative crust. Often one of these elements dominates the clinical pattern. For instance, in some children there is little overt hair loss, the whole infection resembling seborrheic dermatitis. Likewise, in some ectothrix infections a pustular form of dermatophytosis, or kerion, develops. This is less common in endothrix infections. In most kerions the pustules are not a sign of secondary bacterial infection, ²⁸ although this may occur under adherent crusts.

Tinea capitis is rare in adults, although it may occasionally be found in elderly patients and is caused by a variety of fungi such as T. tonsurans. It has been associated with scarring alopecia of unknown etiology (pseudopelade) in adults.

In favus the same processes occur, but an important clinical characteristic is the formation of an inflammatory crust, or scutulum, composed of neutrophils and serous exudate around individual hair shafts. With time these amalgamate over the surface of the scalp so that the hair appears to be matted together with a thick crust that is said to have a mousy odor. In many patients the signs are indistinguishable from those seen with other forms of scalp ringworm. Two other characteristics of favus are late shedding of hairs and a tendency to develop scarring alopecia. The infection may persist into adult life, particular in women.

Untreated scalp ringworm usually remits spontaneously after puberty. Permanent hair loss is uncommon unless there has been a severe inflammatory response or the patient has favus. A surprising degree of recovery of hair growth occurs, even in children with severe kerions.

Tinea capitis has to be distinguished from seborrheic dermatitis, which usually occurs in older children and does not cause hair loss. Alopecia areata also causes circumscribed areas of hair loss but does not scale, and the exclamation mark hairs seen in this condition broken hairs tapering from the fractured end toward the skin surfaceare pathognomonic.

Onychomycosis, or fungal infection of the nails, usually occurs in individuals with infections of adjacent toe or palmar skin, except in rare cases of childhood nail infection in which nail plate invasion may develop without skin involvement. There are several different patterns of nail plate invasion. ²⁹

The most common clinical pattern of onychomycosis is distal and subungual onychomycosis, in which the nail plate is invaded from the distal and lateral borders. There is usually associated thickening of the nail, which becomes white, yellow, or brown. The latter color is more common in the rare instances of T. mentagrophytes nail disease. In onychomycosis caused by endothrix scalp fungi such as T. soudanense, the thickening may be minimal, and the nail surface is pitted with small fissures. ³⁰ The most common cause of onychomycosis is T. rubrum, which often accompanies long-standing disease, and the infection involves the entire nail plate.

Superficial white onychomycosis occurs where the nail plate is invaded from the top surface, which is eventually covered with white crumbly plaques. Other fungi, such as Fusarium species, more commonly cause this pattern of nail invasion but this may be followed by deeper penetration. However, in its pure form superficial white onychomycosis can be seen with T. mentagrophytes, and it may also accompany distal and subungual onychomycosis in some T. rubrum infections.

Rarely, invasion appears to originate from the proximal nail plate. This is usually a feature of relapse of treated nails, but rapidly spreading proximal nail plate invasion has also been described in patients with AIDS. ³¹

Onychomycosis can occur at any age, although it is more common with increasing age. Males and females are equally affected.

This infection has to be distinguished from onychomycosis caused by Candida, in which there is little nail plate thickening but toenail infection is rare. Scytalidium infections may also lead to nail plate invasion. These are difficult to distinguish from infections caused by dermatophytes, but the nail plate is often not grossly thickened and may be severely undermined, and invasion predominantly affects the lateral border of the plate in the early stages of disease. Psoriasis of the nail also causes onycholysis, but the nail plate is typically covered with fine pits.

On rare occasions patients known to be immunocompromised or apparently unselected individuals develop dermatophyte infections in which the fungi invade subcutaneous tissues via the lymphatics, usually causing clusters of granulomas, lymphedema (Fig. 265-5) , and draining sinuses. ³² Sometimes aggregates of fungal hyphae resembling those found in eumycetomas may be seen in histologic sections. These dermatophyte pseudomycetoma grains may be surrounded by neutrophil abscesses, but often the fungal hyphae are engulfed by giant cells in tissue sections. Deep dermatophyte infections may extend further to involve draining lymph nodes or other sites, including the liver and brain, and they may be fatal.

The immune mechanisms in dermatophytosis may lead to the appearance of secondary rashes called id reactions. The most common of these is a type of acute vesicular eczema or pompholyx that occurs on the hands and feet in patients with inflammatory ringworm of the feet, mainly caused by T. mentagrophytes. These events are thought to be linked if the original dermatophyte infection becomes inflamed before the appearance of the secondary rash, the latter is maximal on the affected foot, and the patient has a strong delayed-type hypersensitivity reaction to intradermal trichophytin. The histology of this id reaction is that of eczema. A second form of id reaction is seen in patients with inflammatory tinea capitis or corporis and is usually caused by zoophilic organisms. It consists of small follicular papules, some of which appear necrotic. This is a form of cutaneous vasculitis that usually subsides spontaneously. Both reactions may be triggered by antifungal therapy. Other less common types of id reaction include annular erythema and erythema nodosum.

Patients with follicular invasion by dermatophytes may develop a residual granuloma in the late stages of the disease called Majocchis granuloma. It is usually sterile, although sometimes fragments of mycelium can be seen in histologic sections, and resolves slowly with time.