Introduction
Background
Favus, also termed tinea favosa, is a chronic inflammatory dermatophytic infection usually caused by Trichophyton schoenleinii.1,2,3 Rarely, favus is caused by Trichophyton violaceum, Trichophyton mentagrophytes var quinckeanum, or Microsporum gypseum. Favus typically affects scalp hair but also may infect glabrous skin and nails. The causative agent of mouse favus is T mentagrophytes var quinckeanum, also termed Trichophyton quinckeanum, which can cause favus in humans, although rarely.4,5
Pathophysiology
Favus is a superficial dermatophyte infection usually caused by T schoenleinii. In most patients, favus is a severe form of tinea capitis; however, it may occur, although rarely, as onychomycosis, tinea barbae, or tinea corporis.
Favus is 1 of 3 primary patterns of hair infection (ectothrix, endothrix, favus). Typically, hair is not as heavily infected as in trichophytosis caused by Trichophyton tonsurans. Hair is able to grow, and frequently, long hairs are observed in the disease state. The most characteristic feature is the formation of air spaces between hyphae within the infected hair. These air spaces (air tunnels) form as a result of autolysis of the hyphae. Arthroconidia rarely are seen within the hair. Such infected hair commonly is termed favus-type hair. In the sera of patients, antibodies to causative fungi are found by charcoal agglutination and immunodiffusion assay; however, the exact role of antibodies is not clear.6
Frequency
United States
Favus is uncommon in the United States, although foci have been described in past decades in rural areas of West Virginia, New York, Kentucky,7 and Arkansas. Favus often is seen in geographic regions where lifestyles are associated with malnutrition, neglect, and poverty.
International
Foci of favus have been seen worldwide, including Poland,8 Southern and Northern Africa,9 Pakistan,10 the United Kingdom, Australia, South America (Brazil),11,12 Canada (Quebec),13,14 and the Middle East.
Mortality/Morbidity
Permanent alopecia with scarring often follows favus, which is a chronic disfiguring infection.
Race
Favus shows no racial or ethnic preference.
Sex
Both females and males may be affected equally; however, some report a slight predominance of female patients with favus.
Age
Favus appears in both children and adults. Favus usually is acquired during childhood or adolescence and typically persists into adulthood.
Clinical
History
Favus usually begins on the scalp, often in childhood, and persists for many years as unsightly, crusted plaques. According to the severity of the disease, 3 main stages are described.
- First stage: Only erythema of the scalp is seen, primarily around follicles. Hairs are not loose or broken.
- Second stage: Formation of scutula is seen with the beginning of hair loss.
- Third stage: The most severe stage involves large areas of the scalp (at least one third); extensive hair loss, atrophy, and scarring result. Formation of new scutula at the periphery of plaques is common.
Physical
The scutulum, a yellow cup-shaped crust that surrounds a hair and pierces its center, is characteristic. Scutula form a dense plaque, each composed of mycelia and epidermal debris. Often, a secondary bacterial infection occurs in the plaque. Plaque removal leaves an erythematous moist base. The dense masses of yellow crusts may be solitary or numerous, and in patients who are severely affected, involve the entire scalp. A mousy odor typically is present. Glabrous skin may show similar yellow crusting.
On glabrous skin, favus is a papulovesicular and papulosquamous eruption in which typical scutula may be evident. As an onychomycosis, tinea favosa resembles other forms of tinea unguium.
In addition to typical scutular favus on the scalp, several atypical manifestations of favus have been described.
- Favus pityroides mimics dandruff or seborrheic dermatitis. Numerous small-to-large scales are present. On the surface, scales are loose; however, deeper layers are attached strongly to the base. Removal of scales uncovers reddish, moist, and scarring areas of skin.
- Favus psoriasiformis is a psoriasis-imitating favus, both on the scalp and on glabrous skin. Instead of yellowish scutula, patients present with whitish scales mimicking the typical lesions of psoriasis.
- Favus follicularis is characterized by cone-shaped wax-colored papules around the follicles. Hair shows the typical features of favus.
- Favus impetigoides is characterized by yellowish (honey-colored) crusts imitating impetigo that are located on the scalp. Frequently, they form larger plaques that do not improve with antibacterial treatment. The characteristic mousy odor and dull hair suggest the diagnosis of favus.
- Favus papyroides is characterized by small loci on the scalp that are covered by a brittle substance similar to parchment. Beneath, typical small scutula may be present.
- Favus herpetiformis is an atypical variant of favus corporis. Round, erythematous, scaling plaques with small papules, vesicles, pustules, and/or crusts on the border are located on the trunk and extremities. This form of favus shows an annular shape and resembles the lesions typical of tinea corporis.
Tinea favosa of the scalp shows erythematous lesions with pityroid scaling. Some hairs are short and brittle.
Favus of the scalp shows extensive lesions with scarring alopecia.
Black man, aged 45 years, with favuslike yellow crusting of scalp. Potassium hydroxide and fungal culture were negative.
Causes
Primarily caused by T schoenleinii, favus rarely may be caused by T violaceum, T mentagrophytes var quinckeanum, or M gypseum. Although vertical transmission may occur, family attack rates are highly variable. Most evidence suggests that favus is not a highly contagious disease.
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References
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Further Reading
Keywords
favus, tinea favosa, favus honeycomb ringworm, tinea favosa capitis, Trichophyton schoenleinii, T schoenleinii, Trichophyton violaceum, T violaceum, Trichophyton mentagrophytes var quinckeanum, Microsporum gypseum, M gypseum
