Favus or tinea favosa is a severe and chronic inflammatory dermatophyte infection, due in most cases to Trichophyton schoenleinii. Historically, the term ‘favus’ had been used, at the beginning of the nineteenth century, to characterize the honey-like exudate in some scalp infections. Then, in 1839, the fungal etiology of this condition was discovered by Johann Lucas Schoenlein. This notorious kind of tinea capitis used to be highly frequent globally, mainly in impoverished countries. Nowadays, it has become a historical form, except in some areas in Asia and Africa.
Clinically, favus is characterized by scutula (yellow saucer-shaped crusts consisting of hyphae and scales) around hair follicles and severe scarring alopecia, which can lead to considerable psychosocial problems. Besides the scalp, it may infect the glabrous skin (skin that is devoid of dermal filaments) and nails.
Trichophyton schoenleinii accounts for about 95% of favus cases. However, in rare instances, zoophilic (Microsporum canis, Trichophyton mentagrophytes var quinckeanum and Trichophyton verrucosum), geophilic (Microsporum gypseum) and other anthropophilic (Trichophyton violaceum) species have been recovered from favic lesions. Transmission of the infection takes place indirectly via loose strands of hair and desquamated epithelial cells, then through direct contact between affected family members and intimate friends. Favus-associated dermatophytes are especially disseminated by sharing towels, clothing, barbershop instruments, and hairbrushes.
In the nineteenth and early twentieth centuries, favus was widely spread in southern Africa, Mediterranean regions, Pakistan, the United Kingdom, Australia, and South America. It occurred in micro-endemic clusters, with a high risk of family transmission, in geographic areas where there are poverty and poor hygienic conditions. Until the 1950s, the infection was a major health problem due to the lack of effective treatment.
With the approval of griseofulvin in 1958, general improvement of living conditions, and anti-favus campaigns, favus caused by T. schoenleinii was almost eradicated in most nations like the USA and European countries. Nowadays, the infection is still an unsolved epidemiological problem with endemic areas in Nigeria, Ethiopia, Western China, Iran, and some regions of India. The disease still occurs sporadically in Turkey, western Europe, and South America. Therefore, favus is present but is likely misdiagnosed because of the emergence of atypical presentations.
Tinea capitis favosa occurs predominantly during childhood, mainly because of their lack of fungistatic long fatty acids in the sebum. Its incidence rate is higher in boys, probably due to shorter hair, which allows easy access for circulating spores. Menopausal women are frequently involved by adult tinea capitis likely because of sebaceous glands involution due to decreased blood estrogen levels during menopause.
Tinea Capitis Favosa
Favus is the most severe clinical type of tinea capitis. It has an insidious course, without an acute phase, leading to the diagnosis delay. In 95% of cases, favus begins with folliculocentric erythemato-squamous areas. If these lesions are removed, scutulum starts to develop. It is typically a cup-shaped yellow crust on the scalp centrally pierced by dull grey hair, with underlying erythema. Affected skin is characterized by a mousy or cheesy odor. Wood’s light examination usually reveals bright green fluorescence. Secondary bacterial infections can occur with pus and lymphadenopathy. As the disease progresses, many scutula coalesce to involve more than one-third of the scalp. Untreated, favus is classically slowly progressive. The parasitized hair will fall out, causing extensive permanent alopecia, atrophy, and scarring.
Favus of the Glabrous Skin
Tinea favosa of the glabrous skin and nails are reported in only 7% of cases. Clinically, favus of the glabrous skin presents as papulovesicular and/or papulosquamous circinate eruptions in which typical scutula may be evident. The crusts may be multiple and large. Skin atrophy may be noticed in affected areas, which is unusual in typical tinea corporis. The scrotum is one of the commonest involved sites.
Nail involvement was noticed in 2.4% of cases of favus. It is indistinguishable from other forms of onychomycosis. Individuals infected their fingernails accidentally when epilating the infected scalp of other persons. Favus of fingernails was a major source for reinfection of the scalp when patients were treated by radiotherapy, but currently, auto-inoculation is considered very rare in cases of T. schoenleinii infection.
Generalized involvement of favus on the scalp and glabrous skin was common during the nineteenth and early twentieth centuries. With the improvement of living conditions, cases were only reported in poor and rural areas. It represents only 1 of 806 (0.1%) cases of tinea favosa. Systemic favosa is extremely rare. Mucous involvement, gastroenteritis, esophagitis, keratitis, and endophthalmitis are the reported manifestations.
In up to 5%, the classic scutular form of favus is replaced by atypical clinical features including pityroid, papyroid, follicular, impetiginous, and psoriasiform form without alopecia. These atypical presentations cause a delay in diagnosis and treatment.
Direct microscopic examination of infected hairs mounted on slides with 10% potassium hydroxide (KOH) reveals endothrix infection. Mycelium and chains of spores are shown within the shafts. The most characteristic finding is elongated air-spaces seen at the sites of hyphae that had undergone autolysis. A fungal culture is the most informative method for diagnosing favus. T. schoenleinii should be cultured on Sabouraud glucose agar. The colonies are waxy or downy with ramifications, cerebriform, deep cream in color on the surface, tan-colored on the reverse, and slow-growing between two to four weeks. KOH examination of the favic culture reveals characteristic antler-like hyphae, chandelier structures, and mycelia with intercalary or terminal chlamydospores terminal dilation of hyphae giving a nail head shape known as favic nails.
The polymerase chain reaction (PCR) test has been recently used for the diagnosis of this rare mycosis. It may be a good alternative when fungal culture is unsuccessful.
Management of favus was challenging in the early nineteenth, based on radiotherapy. Since 1958, oral griseofulvin had been the treatment of choice for anthropophilic Trychophyton infections, particularly tinea capitis favosa. The appropriate dosage was 1 g/day for an adult of average size and 15 to 20 mg/kg/day for children, during 6-8 weeks, but now larger doses and longer treatment duration are required. T. schoenleinii resistant to griseofulvin has been isolated. The thick, multiple-layered cell wall of the fungi could act as a barrier impermeable to griseofulvin. (Khaled : (14)
In addition to decreased efficacity, griseofulvin has potentially severe side-effects such as carcinogenicity and teratogenicity. Currently, newer antifungal drugs like terbinafine and azoles are recommended. They have the advantage of shorter treatment with a more favorable risk-benefit ratio and persistence in fungicidal concentrations for several weeks after completing the course of treatment, which prevents reinfection.
The local treatment, which is an adjunct to systemic therapy includes removing the crusts, cutting of hair around the alopecia patches, and applying twice a day antifungal shampoo, foam gel, lotion, or spray with isoconazole and ketoconazole.
Nail involvement requires more prolonged therapy.
The success of therapy is confirmed by repeated negative fungal cultures.
Favus is the most severe clinical type of tinea capitis. It is a chronic mutilating disease with serious familial and social implications.
The characteristic type of hair invasion in favus (endothrix infection) contributes to the chronic course of the favus, which persists as long as there is hair. Tinea favosa usually occurs in children and adolescents and persists throughout adult life in the absence of treatment.
The treatment outcome varies with the stage at which the condition is diagnosed. With early diagnosis and proper therapeutic management, favus will cure without sequelae. However, late treatment leads to the ultimate scarring alopecia in all clinical presentations.
Every effort should be made to look for an infesting family or school environment. Asymptomatic individuals should be treated simultaneously since the disease may go unnoticed, and T. schoenleinii can shed spores for many years leading to spread.
General improvement of scalp hygiene also represents a fundamental aid to reduce the burden of pathogens. The sharing of combs or hats should be avoided.
All family members should be educated about the importance of seeking medical attention promptly and compliance with medication.
Although favus is very rare today, clinicians should educate the caregivers about the clinical and mycological features of favus. Indeed, this mutilating disease can leave definitive scars if not managed by an interprofessional team.
Most patients present first to primary care providers. If there is any doubt about diagnosis or management, the patient should be referred to a dermatologist. The key is proper diagnosis and initiating prompt systemic therapy, which arrests the disease in an early stage.
Specialty care nurses and pharmacists should cooperate to educate the patients or parents on maintaining good personal hygiene. It is important to clear away the scalp debris, remove the crusts and wash hair, hands, pillows, and bed linens regularly. Children should avoid sharing their personal care products. Pharmacists should verify patient compliance and drug-drug interactions as these are common with oral antifungal agents. The disease is known to be disfiguring. Therefore, consulting a mental health counselor can help patients overcome emotional issues.
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