Dermatophyte infection

Dermatophyte Infection

(Dermatophytoses)
By
Dr.Alaa Al-sahlany
Nov. 4, 2018

Introduction

Dermatophytoses are fungal infections caused by three genera of fungi that have the ability to invade and multiply within keratinized tissue (hair, skin and nails):include

(1) Trichophyton
(2) Epidermophyton
(3) Microsporum

Epidemiology

Trichophyton rubrum is the most common dermatophyte worldwide

Occur most frequently in postpubertal hosts except tinea capitis which occurs mainly in prepubertal children


Men tend to more frequently have tinea cruris and tinea pedis than women

Pathogenesis

First step
Clinical features
Mode of transmission
Type
Non-inflammatory to mild inflammation, chronic
Human to human
Anthropophilic
i.e. T. rubrum
Moderate inflammation
Soil to human or soil to animal
Geophilic
i.e. M. gypseum
Severe inflammation, acute
Animal to human
Zoophilic
i.e. M. canis, T.verrucosum


Host factors
Dermatophyte factors
Protease inhibitor: limit the extent of invasion by inhibiting keratinase
Keratinase : break down keratin and help the fungi invade skin
Sebum has an inhibitory effect on dermatophyte
Mannans in cell wall: has immuno-suppressive effect and inhibit the epidermal proliferation that prevent sloughing off of fungi
Diseases that affect barrier function i.e. icthyosis , Hailey-Hailey disease and Darier disease predispose the skin to infection

Second step

Third step
Once dermatophytes have invaded the skin with help of dermatophyte factors mentioned in the box, three factors limit the infection to stratum corneum:

(1)Preference of dermatophyte for Cooler temperature at skin surface,(2) serum factors such as ferritin and β-globulin that inhibit dermatophyte growth and(3) immune system

Causative pathogen

Type of dermatophyte infection
• Any dermatophyte but T.rubrum is the most common

Tinea corporis, tinea pedis, tinea cruris, tinea manuum, tinea faciei and tinea unguium

T.Tonsurans is the most common in USA
T.Verrucosum is the most comon in Iraq


Note: favus is caused by T. schoenleinii.
Tinea capitis

Tinea corporis

Infection of the skin of the trunk and extremities, excluding the hair, nails, palms, soles and groin

Any dermatophyte can cause it BUT T. rubrum is the most common pathogen

Infection spreads centrifugally from the point of skin invasion, with central clearing of the fungus , typically resulting in annular lesions

Variants:

Tinea incognito: tinea lesion modified by topical steroids, may lack a raised scaly border and clear center.

Majocchi’s granuloma: is characterized by follicular papulopustules or nodules, commonly seen in women who have tinea pedis or onychomycosis and shave their legs. Topical steroids and immunosuppression are predisposing factors.

Tinea cruris(Jock itch)

Infection of the inguinal region
Any dermatophyte can cause it BUT T. rubrum is the most common pathogen
This disease is more often seen in men than in women, since the scrotum provides a warm and moist environment that encourages fungal growth
The inflicted are more likely to have tinea pedis and onychomycosis as a source of dermatophytes

Other predisposing factors include obesity and hyperhidrosis

Presented as a sharply demarcated with a raised, erythematous, scaly active border that may contain pustules or vesicles and a central clearance

The scrotum itself is generally spared, unlike candidiasis of groin

Tinea manuum
Infection of the palm and interdigital spaces

It is different from that of back of hands due to lack of sebaceous glands on the palms

.

Usually non-inflammatory and often unilateral there is diffuse hyperkeratosis of the palms and digits with accentuation of scales on creases that fails to respond to emollients

An important clinical clue is tinea unguium

Is often present in patients with tinea pedis(two feet and one hand syndrome)

Tinea pedis(Athlete’s foot)

Infection of the soles and interdigital web spaces of the feet

More common in adults

Lack of sebaceous glands and moist environment
due to occlusive shoes are predisposing factors

Tinea pedis is uncommon in populations that do not wear shoes although the barefoot people can acquire the fungus in public facilities i.e. gym

The feet are the most common location for dermatophyte infections

Types:

(1)Moccasin: diffuse hyperkeratosis, scaling and erythema

(2)Interdigital :Most common type; erythema, maceration, fissures and ,ulceration between toes

Moccasin

Tinea barbae
Involves the bearded areas of the face and neck in men

Two types:

(1) The inflammatory type: develops slowly and produces nodules and kerion-­like swellings: acquired from animal, caused by T. verrucosum.





(2)Non-inflammtory type: less inflammatory, characterized by pustular folliculitis , caused by T. rubrum. Aquired from contaminated razors in barber- shops. Now less common owing to use of disposable instruments and disinfectant

In both types: the hairs are either easily plucked or lost.

Tinea faciei
Infection of face

The same as tinea corporis

Typical annular rings are usually lacking and the lesions are exquisitely photosensitive. Therefore, misdiagnosed

Tinea capitis

A common dermatophyte infection of the scalp in children, whereas adult infection occurs infrequently

T. tonsurans is currently the most common cause of tinea capitis in the US while T.verrucosum in Iraq

The “carrier state” of tinea capitis is contagious through contaminated brush, hat, towel and barber tools

Types of dermatophytes that invade hair:

(1)Endothrix: exist inside the hair shaft, caused by Trichophyton, non- fluorescent. Exception is T. schoenleinii (fluorescent)

(2)Ectothrix: exist outside the hair shaft, caused by Microsporum(fluorescent) or Trichophyton (non-fluorescent)

Clinical types:

Non-inflammatory:
Gray patch:M. auduinii, present as a dry scaly patch of alopecia


Black dots:T. tonsurans, caused by hair breakage near the surface

Inflammatory:

Kerion: M.canis, present as a boggy, purulent plaques with abscess formation and associated alopecia, patient may become systemically ill with extensive lymphadenopathy

Favus: T. schoenleinii, the most severe type of dermatophyte hair infection, present as a concave, sulfur-yellow crusts pierced by hairs (“scutula”)

Tinea unguium (onychomycosis)

Infection of the nail unit
Three types : based upon the point of fungal entry into the nail unit

Distal/lateral subungual: (most common)

Superficial white:

Proximal subungual: ( seen frequently in immunocompromised hosts).

Multiple nails on one or both hands or feet are usually affected

Affects men more often than women?

Frequently associated with chronic tinea pedis

Toenail infections are considerably more common than fingernail?

Clinical features:

Hyperkeratosis of nail bed

Thickenening and yellowish discoloration of nail plate

Onychlysis (seperation of nail plate from nail bed)

Nail dystrophy when the entire nail plate and bed are involved

Diagnosis

Clinical examination(most important)


KOH examination of skin scraping(by blade), nail clipping (by nail clipper) or hair plucking(by tweezer)

Wood’s lamp(ultraviolet light of 365 nm wavelength): Infected hairs show bright green or yellow- green fluorescence

Culture:2-4 weeks

Biopsy: we see hyphae in stratum corneum

Treatment

Topical antifungals e.g. ketoconazole, clotrimazole are the first line treatment

Systemic antifungal: indications

(A)tinea manuum, (B)mocassin type of tinea pedis, (C)tinea capitis, (D) tinea barbae, (E) tinea unguium, (F) when extensive area is involved


Antifungals

Comment

Spectrum of action
Antifungal agent
In general, the longest course of treatment is for tinea unguium followed by tinea capitis followed by other types of dermatophytosis

Griseofulvin is the first choice for treatment of tinea capitis (4-12 weeks course)

Imidazoles and allylamines are the first choice for treatment of tinea unguium

Dermatophytes, Candida and Pityrosporum
• Imidazoles e.g. ketoconazole, itraconazole, fluconazole, clotrimazole:

Dermatophytes

• Allylamines e.g. terbinafin

Candida only

• Polyenes e.g. amphotericin B and nystatin

Dermatophytes only

Griseofulvin

Dermatophytid(id reaction)

Associated with inflammatory tinea capitis and acute tinea pedis

Represent a systemic reaction to fungal antigens

Diagnosis requires:(1) finding of fungus at site remote from the lesions of the dermatophytid, (2)the absence of fungus in the id lesion, and(3) involution of the lesion as the fungal infection is treated

Definitions

Gyrate:revolves or spin around a fixed point or axis
Polycyclic:having two or more rings fused together
Serpiginious: having a wave border (snake-like)
Circinate:circular or round
Annular: ring-like