2.3.1 Dermatophyte Infections
Grading & Level of Importance: A
Tinea, the term is usually followed by the latin name for the involved anatomic site such as Tinea corporis (body), Tinea capitis (scalp), Tinea faciei (face) and for other.
- Tinea corporis and tinea capitis: more common in children.
- Favus: rarely found.
- Tinea barbae: exclusively in males.
- Tinea pedis and onychomycosis: 20% prevalence among adults.
- Tinea manuum: almost always following tinea pedis.
Infections caused by dermatophytes (keratinophilic fungi which infect hair, nails, and scales) of the species Microsporum, Trichophyton and Epidermophyton. Transmission: human-human and animal-human (more inflammatory).
Mycoses are often divided into 3 classes: dermatophytes, yeasts, molds.
Aetiology & Pathogenesis
- Anthropophilic dermatophytes (T. rubrum): little inflammatory chronic infection.
- Zoophilic types (Mycrosporum canis, Trychophyton verrucosum): an intense inflammation.
- Geophilic species: rarely cause mycoses in humans.
Signs & Symptoms
- Tinea in the skin usually presents with annular, erythematous, circumscribed plaques with peripheral scale (caused by the spread of the fungus within the stratum corneum); centrifugal growth with tendency toward central clearing. Itching is variable. Occasionally dyshidrosiform or pustular when caused by zoophilic agents.
- Trichomycoses: dermatophytes of terminal hairs, clinically one should distinguish between Trichophyton infections (classic tinea capitis or scalp ringworm), Microsporum infection and Favus. Trichomycoses are caused by spread of the agent from the stratum corneum into hair follicles and shafts; only anagen hairs are affected.
- Classic Tinea capitis is the most common dermatophyte infection in childhood. In anthropophilic endothrix infection, the hair is filled with spores, visible as small black dots in the follicle opening ("black dot ringworm").
- Zoophilic dermatophytes extend deep into the follicles and induce an intense inflammation, pustules and massive purulent secretion ("kerion").
- Microsporum infections often lead to bland deep folliculitis without abscessformation caused by anthropophilic M.audouinii or by M.canis (zoophilic; particularly in cats). Hairs break off shortly after emerging above the scalp surface. These hairs fluoresce yellow-green on Wood’s light examination.
- Favus: features exuberant masses of fungal elements, scales and secretions producing scutula (Latin for small shield). They heal with scaring (cicatricial alopecia or pseudopelade). Tinea barbae: deep abscess-forming folliculitis of the beard hair caused in particular by T. verrucosum (common dermatophyte in cows) or the zoophilic form of T. interdigitale.
Ringworm of the palms and soles; Tinea pedis is one of the most common dermatological diseases. There are 3 clinical forms:
- Interdigital: maceration and coarse scaling, most commonly between closely approximated 3rd and 4th toes. Shedding of the macerated skin produces erosions and fissures.
- Hyperkeratotic: non-inflammatory diffuse scaling of the entire plantar surface of soles; often mistaken for dry skin.
- Vesicular/dyshidrotic: most often on the arch of the foot, as well as the tips of the small and great toes. Presents with scattered, intensely pruritic vesicles which may be cloudy.
Tinea manus; usually only affects one hand, but may be bilateral in chronic cases, clinically there may be fine collarette scaling on the cup of the palm, especially along the palmar creases.
Dyshidrosiform type: itchy vesicles on palm and sides of fingers. Special type: one-hand/two-feet mycosis which always affects both soles as well as one palm. Onychomycosis (tinea ungium): More than 80% of all nail infections are caused by dermatophytes (usually T. rubrum). Impaired nail growth is a predisposing factor. More frequently affects the feet (starting from tinea pedis) rather than the hands. Several forms of fungal nail infection can be clinically distinguished:
a) unilateral subungual onychomycosis is the most common form,
b) white superficial onychomycosis (white macules),
c) proximal subungual onychomycosis,
d) complete dystrophic onychomycosis with marked destruction of the nail plate as final state of the first three forms.
Laboratory & other workups
Identification of fungi (KOH examination -> immediate result; culture -> takes 3-4 weeks, PCR
Clinical features, mycology laboratory.(KOH examination detects fungal elements but does not identify species); Culture: takes 1-4 weeks; PCR: just 24 hours)
Prevention & Therapy
- General measures include correction of predisposing factors (sweating, improper shoes), treatment of (asymptomatic) carriers.
- Antimycotics: azoles, amorolfine, ciclopirox olamine, terbinafine.
Polyenes (amphotericin B, nystatin) are ineffective against dermatophytes.
Keratolytics: salicylic acid, urea (nails, hair). Fabry's tincture (salicylic acid, phenol). Formalin to disinfect shoes.
- For systemic therapies terbinafine is the gold standard; alternatively, triazoles such as itraconazole, fluconazole can be used. Griseofulvin is restricted to Microsporum infections in childhood.
- What are the possible causes of this nail dystrophy?
- Statement 1 If tinea capitis is suspected, the scalp should be examined with Wood light
- What are the differential diagnostic considerations here?
- A 20-year-old woman with hay fever has three house cats. The pictured lesion has been present for 3 weeks. Which additional studies are required?
- This farmer spent August at a Alpine mountain farm cabin with his cows and a few mosquitoes. The skin lesion shown in the picture appeared in mid-August. It is asymptomatic but spreading. What is your diagnosis?
- Which of these factor predispose to tinea capitis?
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