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Tinea capitis
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Figure 1: Diagram showing the methods of fungal invasion of the hair shaft
Figure 2: Tinea capitis of the dry type caused by M. canis infection
Figure 3: Tinea capitis of the kerion type caused by T. verrucosum infection
Figure 4: Tinea corporis showing a typical scaly edge and healing centre
Figure 5: Widespread tinea corporis
Figure 6: Tinea cruris
Figure 7: Tinea pedis showing maceration and a fissure in the toecleft
Figure 8: Fungal nail infection showing subungual hyperkeratosis
Figure 9: Fungal nail infection showing thickening and discolouration of the nail plate
Figure 10: Oral candidosis or "denture sore mouth"
Figure 11: Seborrhoeic dermatitis showing greasy scale in the nasolabial fold
Figure 12: Pityriasis versicolor in light skin
Figure 13: Pityriasis versicolor in dark skin
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Infection of the scalp can occur in one of three ways (Figure 1) and is dependent upon the species of dermatophyte involved. Ectothrix infections occur when both the inside and the outside of the hair shaft are invaded and Microsporum canis, Microsporum audouinii, Trichophyton mentagrophytes and Trichophyton verrucosum can cause this type of infection. Ectothrix infections are clinically very obvious and occur as a dry scaling patch of alopecia (M. canis, M. audouinii) or as boggy inflammatory swelling known as a kerion (T. verrucosum, T. mentagrophytes). Endothrix infections where only the inside of the hair shaft is invaded are often much more discrete although chronic infection will ultimately lead to a good deal of alopecia. Trichophyton tonsurans, Trichophyton violaceum and Trichophyton sudanense are all common endothrix infections. The thirdtype of hair invasion is known as favus and is caused by the single dermatophyte Trichophyton schoenleinii. The type of invasion here is unique to this fungus and results in the inside of the hair shaft containing both fungal elements and significant air pockets which gives rise to cup shaped crusts known as scutula. Favus is now a relatively uncommon disease seen only in third world countries although may still occasionally exist in long-stay institutions such as mental hospitals, children's homes, prisons and in the military.
Zoophilic scalp infection regularly occurs in a sporadic fashion; Microsporum canis (Figure 2) and Trichophyton verrucosum (Figure 3) are the commonest species seen simply because they have domestic animals as primary hosts. The prevalence of anthropophilic infection has varied considerably over the past century. Prior to the advent of systemic antidermatophyte agents, the only method of treatment was epilation. Although effective, patients were not happy to volunteer for such treatment and disease prevalence remained quite high. The introduction of the drug griseofulvin in the late 1950's revolutionised the treatment of scalp infection and rendered epilation unnecessary. As a result anthro-pophilic scalp ringworm secondary to Microsporum audouinii became very much less common in the developed world although the incidence remained, and still remains, high in countries where drug availability is limited. Tricophyton violaceum, an ectothrix infection found in the Middle East, the Indian subcontinent and parts of the Far East has always been fairly prevalent, and has spread much more widely following immigration patterns. More recently, Trichophyton tonsurans infection, which is also endothrix, has reached almost endemic proportions in a number of western countries, notably the USA and the UK.1 The reasons for this are not entirely clear although the disease is certainly most common in patients of afro-caribbean origin. This fungus produces the so-called "black dot" variety of scalp ringworm where the hair breaks off at the scalp surface leaving small dark areas which represent the mouth of hair follicles.
Zoophilic species produce a much greater inflammatory response and this often results in a boggy inflammatory swelling known as a kerion, which is mistreated as a bacterial abscess. This invariably leads to an area of scarring alopecia as the kerion resolves. It is therefore important to consider a fungus as a cause of any abscess like swelling of the scalp or indeed other sites, particularly when the lesion is multiheaded. The pus contained within such lesions is rich in fungal elements which can easily be visualised microscopically. Early intervention with antifungal drugs is generally effective and helps to minimise the risk of scarring.
Tinea corporis
Infection of the glabrous skin of the trunk and limbs is usually the result of an anthropophilic or zoophilic infection. Typically the lesions are ring like with a raised scaling edge and a healing centre (Figure 4). The edge can be irregular and untreated lesions can become very large (Figure 5). Sometimes, satellite lesions, which are also annular, develop beyond the edge of the main lesion. Untreated disease may eventually involve almost the whole of the trunk and limbs and give rise to chronic itch.
Annular psoriasis, discoid eczema, pityriasis rosea, granuloma annulare and other annular erythemas are all included in the differential diagnosis. Almost all of these are best treated by topical steroids and the misdiagnosis and mistreatment of Tinea corporis with topical steroids leads to a reduction in itch and scaling, loss of integrity of the ring like edge and the development of granuloma like nodules. This renders the diagnosis even more difficult. Although Tinea corporis is probably over diagnosed and treated with topical antifungal agents, this is a lesser sin than treating a fungal infection with a topical steroid. Topical antifungal drugs will not cause other dermatoses to deteriorate as is the case with topical steroids in fungal infections.
The disease known as Tinea imbricata is worthy of mention simply because it occurs entirely in the tropics and is widespread in Asia, the Pacific Islands and south and central America.2 It is not endemic to Hong Kong but is to certain parts of nearby countries and may therefore conceivably be seen in travellers to the region. It is caused by a single dermatophyte known as Trichophyton concentricum and produces a specific clinical appearance whereby concentric rings develop in each lesion. Each ring is scaly and slightly infiltrated and they can become multiple until eventually the whole body is covered by this extremely bizarre and unique eruption.
Tinea cruris
This disease affects the groin area although theoretically the axillae may also be involved (Figure 6). In temperate countries it is a disease almost entirely confined to males but does occur in females in tropical climates. It is caused almost entirely by anthropophilic dermatophytes which spread from the toeclefts. Trichophyton rubrum, T. mentagrophytes and Epidermo-phyton floccosum are usually causal.
Flexural infected eczema, intertrigo, psoriasis and erythrasma all can have similar clinical appearances and the same therapeutic considerations apply as they do to Tinea corporis.
Tinea pedis
This is the commonest variety of dermatophyte infection and is widely known as athlete's foot. The disease is generally contracted from the floors of communal bathing places. Nowadays, such bathing places are usually leisure facilities, saunas and sports clubs.3 Previously, industrial baths in the coalmining and other heavy industries were a common source of infection. Disease prevalence amongst users of communal bathing places is directly related to frequency of exposure. It follows therefore that prevalence is higher amongst competitive swimmers than amongst regular users who in turn have higher prevalence than casual bathers. Previous studies carried out amongst coalminers suggested a prevalence of around 80% of all workers who have a communal bath once every working day over a lifetime. Regularly used communal bathing places are heavily contaminated with dermatophytes and various studies have revealed the contamination rate to vary between 100 and more then 300 fungal elements per m2 of floor space. Because each of these fungal elements is protected in a small piece of keratin, it is difficult to keep the floors sterile by means of disinfectant which would require to penetrate the keratin and thus be acutely irritant to all users' feet. Foot powders are not useful therapeutically but their use should be encouraged prophylactically.
Tinea pedis almost always affects the fourth toecleft first (Figure 7) and it may remain confined to this site but can sometimes spread to affect all other clefts and eventually the sole and even the dorsum of the foot. When the whole of the foot is involved in this fashion the disease is known as Moccasin tinea pedis.
Tinea unguum
Tinea unguum known as onychomycosis or fungal nail infection results from a spread of the fungus from the toeclefts or soles into the nails. The disease begins at the hyponychium, often laterally rather than centrally, and spreads slowly but relentlessly down the nail bed resulting in separation of the nail plate from the nail bed (onycholysis) and the development of marked subungual hyperkeratosis (Figure 8). Eventually the disease will reach the proximal nail fold and thereafter involve the nail plate (Figure 9) itself resulting in gross thickening, discolouration and occasionally complete destruction of the nail plate. Toenails are affected in about 80% of all cases of onychomycosis but the disease can spread from the toeclefts to the fingernails.4
Dermatophytes, usually T. rubrum, cause 90% of all cases of onychomycosis. Yeast infection secondary to Candida albicans occurs mostly in the fingernails and generally results from separation of the cuticle from the nail plate resulting in chronic paronychia and subsequently nail dystrophy. There has been much debate about the role of non dermatophyte moulds in onychomycosis and there is little evidence that they are primary pathogens but they are well capable of invading already dystrophic nails in a saprophytic fashion. This does not however mean that their eradication will result in any improvement in the clinical appearance as they are behaving simply as saprophytes. In such cases the commonest cause of the primary nail damage is usually a dermatophyte infection although trauma and other nail diseases may be implicated.
The geophilic mould Scytalidium dimidiatum (formerly known as Hendersonula toruloidea) is undoubtedly a primary pathogen of nail in that it is the only non dermatophyte mould which is capable of causing Tinea pedis and is the commonest cause of Tinea pedis in some parts of South East Asia, notably Thailand and it does not appear susceptible to antifungal drugs. It produces a typical black discolouration of the nails.5
Yeast infection
Both Candida yeasts and pityrosporum yeasts can cause disease of the skin and mucous membranes in certain circumstances.
Candidiasis
Candida yeasts are predominantly commensals of the mouth, vagina and GI tract and have a predilection for mucous membranes. Only under certain circumstances of diminished host defence do they cause disease in these sites. Cutaneous candidiasis is virtually unknown in immunocompetent individuals although diabetics and occasionally patients on antibiotics may develop flexural candidiasis which can be submammary, axillary or occur in the groin area. The lesions are clinically fairly typical and white plaques are seen at the edge of inflammatory lesions.
Oral candidiasis is sometimes the result of long-term antibiotic therapy but is most often seen in patients with dentures who do not sterilise them in a proper fashion and chronic oral candidiasis, known as "denture sore mouth" results (Figure 10).
Vulvovaginal candidiasis is generally outwith the scope of an article on the skin manifestations of fungal disease. It can also occur in diabetics and patients on antibiotics but a significant number of females suffer from recurrent vulvovaginal candidiasis who have no obvious predisposing factors. It is assumed that they have a subtle defect in their host defences to yeasts which result in chronic and distressing disease. It is difficult to eradicate but is usually controllable with the right treatment.
Pityrosporum yeast infection
Pityrosporum yeasts are a complex group of organisms, the classification of which is constantly changing. Many now recognise these yeasts as a variety of the Malassezia group. They are often commensals of the scalp and exist asymptomatically in small numbers. Where they overgrow they initially produce scaling of the scalp (dandruff) and ultimately can spread to produce inflammatory lesions of the face, specifically the eyebrows, eyelashes and nasolabial folds (Figure 11). This condition is known as seborrhoeic dermatitis and/or seborrhoeic blepharitis. The cause is not entirely clear but pityrosporum yeasts are lipophilic and therefore tend to affect patients with greasy skins. On the trunk, psoriasiform lesions can develop in the mid chest, usually in males, and is known as petaloid seborrhoeic dermatitis. A low-grade folliculitis sometimes develops, more often in males than females and is known as pityrosporum folliculitis.
The disease known as Pityriasis versicolor is also related to pityrosporum yeast infection and may result from a yeast mycelial shift which occurs sometimes in organisms of this group. Pityriasis versicolor is an interesting condition which can involve the whole of the trunk and the limbs in a "vest and pants" distribution if left untreated. The lesions are primarily a pale cream/ brown colour and appear dark in patients with white skin (Figure 12) and much lighter patients with brown or black skins (Figure 13). In addition the fungus produces azeleic acid which is in itself depigmenting and therefore white areas remain even after successful treatment. Pityriasis versicolor tends to occur most often in hot, sweaty conditions which may be either climatic or occupational. It is not a difficult condition to treat providing the diagnosis is accurately made.6
Diagnosis of fungal infections
Diagnosis is suspected clinically and confirmed by laboratory examination of specimens by microscopy and culture. Ideally this procedure should be followed in all cases, but it must be recognised that, for much of the time, diagnosis is confirmed by therapeutic trial rather than by laboratory tests. There is some utility in this pragmatic approach so long as its limitations are recognised.
Where systemic treatment is prescribed it is as well, for medicolegal as well as medical reasons, to obtain laboratory confirmation of infection. This applies to infection of the scalp, widespread disease of the body and groin and to nail infection. The quality of laboratory diagnosis depends largely upon the quality of the specimen submitted and specimens should be taken as outlined below:
- Specimens from the scalp should include scale from the edge of the lesion together with some hairs and hair follicles. Hairs from within or at the edge of the lesion should be gripped with the forceps and pulled out by the roots and the whole hair submitted along with the skin scales. If a kerion is present then a swab of the pus should be sent to the laboratory along with the skin and hair specimens.
- In Tinea corporis and Tinea cruris scrapings should be taken with a scalpel blade from the scaly edge of the lesion, scraping from in to out. It is sometimes easier to soak the area in saline first and the resulting slurry deposited on the black paper specimen container.
- Fungal nail infection is predominantly a disease of the nail bed and as much of the subungual debris as possible should be obtained preferably from the most proximal area of infection. A fine dental scraper is very good for this purpose. If necessary the nail can be cut back in order to facilitate collection of the specimen. A thickened piece of nail can be included as well.
Small areas of Tinea corporis, Tinea cruris and athlete's foot confined to the toeclefts generally respond well to one or two weeks treatment with a potent topical antifungal agent. Other inflammatory dermatoses which may look similar do not respond at all.
Yeast infections are generally commensal organisms and there is usually little to be gained from laboratory confirmation of infection. Pityriasis versicolor is the exception and is easily diagnosed by microscopy of skin scrapings. The yeast is lipophilic and difficult to grow in culture which is therefore not necessary to confirm the diagnosis. Because the cosmetic appearance takes much longer to resolve than does the infection itself it is politic to confirm the diagnosis and therefore reassure the patient that the treatment has been correct and will ultimately be effective. Scrapings should be taken in similar fashion to those taken from patients with Tinea corporis.
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