Favus

Etiology

Trichophyton schoenleinii accounts for about 95% of favus cases.[5] 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.[1] 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.[6]

Risk factors include:[1][7][8]

• Immunocompromise
• Virulence of the specific dermatophyte (particularly due to keratinolytic proteases)
• Poor hygiene and malnutrition
• Overcrowding
• Poverty
• Little access to health care

Epidemiology

In the nineteenth and early twentieth centuries, favus was widely spread in southern Africa, Mediterranean regions, Pakistan, the United Kingdom, Australia, and South America.[4][9] It occurred in micro-endemic clusters, with a high risk of family transmission, in geographic areas where there are poverty and poor hygienic conditions.[7][10] Until the 1950s, the infection was a major health problem due to the lack of effective treatment.[4] 

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.[4][10] Currently, the infection is still an unsolved epidemiological problem with endemic areas in Nigeria, Ethiopia, Western China, Iran, and some regions of India.[1][3] The disease still occurs sporadically in Turkey, western Europe, and South America.[11] Therefore, favus is present but is likely misdiagnosed because of the emergence of atypical presentations.[12]

Tinea capitis favosa occurs predominantly during childhood, mainly because of their lack of fungistatic long fatty acids in the sebum.[13] Its incidence rate is higher in boys, probably due to shorter hair, which allows easy access for circulating spores.[1] Menopausal women are frequently involved by adult tinea capitis likely because of sebaceous glands involution due to decreased blood estrogen levels during menopause.[14]

Histopathology

Tinea favosa reveals the following histological findings:[1][15][16]

Epidermis 

• Hyperkeratosis surrounding the lesions
• Atrophic epidermis underlying the scutulum
• A mass of spores and hyphae in the stratum corneum, around and within the hairs (endothrix infection), and in the scutulum clearly stained by periodic acid-Schiff (PAS) or Grocott staining
• Well-preserved hyphae in the periphery of infected lesions
• Granular debris and degenerating mycelium in the center of lesions

Dermis 

• Inflammation with neutrophils and lymphocytes, round-cell infiltrate
• Some small cavities between hyphae (degenerated fungi)

History and Physical

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.[2] In 95% of cases, favus begins with folliculocentric erythemato-squamous areas. If these lesions are removed, the scutulum starts to develop. It is typically a cup-shaped yellow crust on the scalp centrally pierced by dull grey hair, with underlying erythema.[17][18] Affected skin is characterized by a mousy or cheesy odor.[18] Wood’s light examination usually reveals bright green fluorescence. Secondary bacterial infections can occur with pus and lymphadenopathy.[13][18] 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.[1][19]

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.[1][19] 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.[10]

Onychomycosis Favosa

Nail involvement was noticed in 2.4% of cases of favus.[1] 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.[1][19]

Generalized Favus

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.[1][20] It represents only 1 of 806 (0.1%) cases of tinea favosa.[16] Systemic favosa is extremely rare. Mucous involvement, gastroenteritis, esophagitis, keratitis, and endophthalmitis are the reported manifestations.[1]

Atypical Presentation

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.[2]

Evaluation

The typical scutula and some simple laboratory tests confirm the diagnosis of favus.[16] A skin scraping can be guided by Wood’s light examination, which reveals dark green fluorescence.[17]

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.[1][16][21]

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.[15]

Treatment / Management

Management of favus was challenging in the early nineteenth century and was 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, for 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.[14](B2)

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.[13][15](B3)

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.[1][17](B3)

Nail involvement requires more prolonged therapy.[19](B3)

The success of therapy is confirmed by repeated negative fungal cultures.[13](B3)

Differential Diagnosis

• Lichen planus
• Lupus erythematosus
• Amiantacea tinea
• Seborrhoeic dermatitis
• Psoriasis
• Kerion celsi
• Impetigo
• Sarcoidosis
• Folliculitis decalvans
• Squamous cell carcinoma mainly in the cutaneous form

Prognosis

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.[1]

The treatment outcome varies with the stage at which the condition is diagnosed. With early diagnosis and proper therapeutic management, favus can be cured without sequelae. However, late treatment leads to the ultimate scarring alopecia in all clinical presentations.[17]

Complications

• Permanent alopecia
• Disfigurement
• Social withdrawal
• Stigmatization
• Side effects of treatment
• Psychological impairment in children