Dermatophytes/Tinea Infections

Tinea infections are a group of diseases caused by fungi infecting keratinized tissue (hair, nails, and skin). These infections are termed dermatomycoses and are caused by the dermatophyte fungi. There are approximately 40 dermatophyte fungi that are part of 3 genera, including Trichophyton, Epidermophyton, and Microsporum. These infections can affect any part of the body but occur most often in warm, moist regions like the groin and the feet. The diagnosis is clinical with characteristic skin findings, but it can be confirmed with microscopy of skin scrapings. The treatment depends on the site and magnitude of infection but typically begins with topical antifungals like the -azole drugs and terbinafine, and it may progress to oral versions of these medications if topical treatment fails.

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Overview

General characteristics of dermatophytes

  • Dermatophytes are filamentous fungi that belong to the genera Trichophyton, Microsporum, and Epidermophyton.
  • Dermatophytes have septate hyphae with chains of conidia.

Classification of tinea infections

Tinea infections are classified and named by the body region affected. 

  • Tinea pedis: 
    • “Athlete’s foot” 
    • Infection of the interdigital webs of the feet
  • Tinea corporis: 
    • “Ringworm” 
    • Infection of the trunk or extremities (excluding hands/feet)
  • Tinea cruris: 
    • “Jock itch” 
    • Infection of the inguinal folds of the groin
  • Tinea unguium (onychomycosis): infection of the nails
  • Tinea capitis: infection of the hair and scalp
  • Tinea manuum: infection of the hands

Pathogenesis

Reservoir

  • Humans
  • Animals
  • Soil

Transmission

  • Direct contact with infected people or animals
  • Indirect contact through a fomite

Host risk factors

  • Walking barefoot in shared locker room
  • Diabetes mellitus
  • Obesity
  • Immunodeficiency
  • Copious sweating
  • Occlusive footwear
  • Trauma
  • Shaving
  • Contact with animals

Pathophysiology

  • Infect keratinized human tissues (e.g., hair, skin, and nails) 
  • Possess proteases that allow for penetration of the stratum corneum
  • Typically remain superficial, involving only the epidermis, because they cannot survive at the normal body temperature of 37℃
  • Metabolize keratin as a fuel source

Clinical Presentation

Signs and symptoms are similar between the tinea infections, with some minor differences depending on the body region affected. Lesions tend to be well-demarcated, annular, peripheral plaques with a rim of scale. They may also have associated erythema and/or maceration.

Table: Comparison of common dermatophyte infections
NameBody regionEtiologyEpidemiology and risk factorsClinical features
Tinea pedis (“athlete’s foot”)Feet, interdigital spaces of toes
  • Trichophyton rubrum
  • T. interdigitale
  • Epidermophyton floccosum
  • Most common tinea infection
  • Adolescents and adults
  • ↑ Risk from public locker rooms
  • Interdigital: pruritic maceration and scaling
  • Hyperkeratotic: diffuse scaling in “moccasin” distribution
  • Vesiculobullous (inflammatory): pruritic, erythematous, bullous eruption on feet
Tinea corporis (“ringworm”)Trunk and extremities (excluding hands and feet)
  • T. rubrum (most common)
  • T. tonsurans
  • Microsporum canis
  • T. interdigitale
  • Direct contact with infected person or animal, usually cat or dog
  • Common among athletes
  • Pruritic, ring-shaped, erythematous, or hyperpigmented plaques with central clearing
  • Spreads centrifugally
  • Extensive involvement may indicate diabetes or HIV infection.
Tinea cruris (“jock itch”)Groin, inguinal folds
  • E. floccosum
  • T. rubrum
  • T. interdigitale
  • Men > women
  • Often spreads from preexisting tinea pedis
  • ↑ Risk with obesity, diabetes, immunodeficiency, copious sweating
  • Involves inguinal folds
  • Erythematous patches spread centrifugally with partial clearing.
  • May spread to perineal and perianal regions
  • Spares scrotum
Tinea unguium (onychomycosis)Fingernails or toenailsT. rubrum
  • Direct contact with dermatophytes
  • Nail injury
  • ↑ Risk with tinea pedis infection
  • Adults > children
  • Discoloration, hyperkeratosis, splitting of nail
  • Subungual debris
Tinea capitisHair follicles and scalp
  • T. tonsurans
  • T. violaceum
  • T. verrucosum
  • M. canis
  • Direct contact with dermatophytes
  • Trauma from an object (i.e., a comb)
  • Scaly plaques with alopecia ± black dots
  • Endothrix infection: fungal spores within the hair shaft
  • Ectothrix infection: fungal spores surrounding the hair shaft
  • Favus infection: fungal spores and air pockets within the hair shaft
Majocchi granuloma (fungal folliculitis)Hair follicles on the bodyT. rubrum
  • Trauma to skin
  • Occlusion of hair follicles
  • Shaving hair
  • ↑ Risk with immunosuppression and corticosteroid use
  • Localized perifollicular papules
  • Erythema or hyperpigmentation
  • Pustules
  • Abscesses or dissemination in immunocompromised patients
Tinea corporis

Tinea corporis, “ringworm” on a child:
Infection is most commonly due to Trichophyton rubrum, which presents with pruritic, erythematous, circular plaques with peripheral scales and central clearing.

Image: “Tinea corporis” by Mohammad3021. License: CC0

Diagnosis and Management

Diagnosis

  • Primarily diagnosed clinically
  • Confirmed by KOH prep:
    • Scale from the periphery of a lesion is scraped onto a glass slide.
    • KOH is applied to the scale.
    • Dermatophytes are identified by visualizing septate hyphae.
  • Fungal cultures are an additional alternative for definitive diagnosis.
  • Onychomycosis can be diagnosed with a PAS stain of nail clippings.
Trichophyton rubrum

Trichophyton rubrum: This 475× magnification of T. rubrum shows centrally grouped, elongated macroconidia with septations. There are also many microconidia in the shape of teardrops.

Image: “Trichophyton rubrum” by CDC/Dr. Lucille K. Georg. License: Public Domain

Management

All variants of tinea are treated with antifungals.

  • Tinea pedis:
    • Topical terbinafine: Terbinafine is an allylamine and works by inhibiting squalene epoxidase.
    • Oral terbinafine for recalcitrant cases
  • Tinea corporis:
    • Topical azoles (e.g., ketoconazole) as initial therapy (azoles work by inhibiting ergosterol synthesis → impair cell wall production)
    • Oral azoles (e.g., fluconazole) for recalcitrant cases
  • Tinea cruris: topical azoles
  • Tinea unguium (onychomycosis):
    • Oral terbinafine
    • Oral fluconazole
  • Tinea capitis:
    • Oral terbinafine for Trichophyton species
    • Oral griseofulvin (inhibition of microtubules) for Microsporum species
  • Majocchi granuloma: oral azoles

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Differential Diagnosis

  • Erythrasma: bacterial skin infection caused by Corynebacterium minutissimum. The presentation of erythrasma is characterized by regions of scaly, pruritic, broken skin. The infection most commonly occurs in the spaces between the toes but may also present in intertriginous areas. It may co-infect with Candida or dermatophytes, making the diagnosis more difficult. Areas of infection appear fluorescent red under a Wood’s lamp. Treatment is with topical antibiotic therapy.
  • Candidal skin infection/intertrigo: infection and inflammation of intertriginous regions, including the folds of an abdominal pannus. Candidal skin infection may be fungal or bacterial, and it typically presents with moist, erythematous patches within skin folds. This condition may eventually lead to skin breakdown. Diagnosis is clinical, and treatment is with topical antifungal therapy.
  • Atopic dermatitis/eczema: inflammatory skin disease that most frequently affects children but can also be present in adults. Eczema is a chronic condition that presents with dry, crusted, erythematous plaques that may be intensely pruritic. The dermatitis most often affects the flexor surfaces and is associated with other types of atopy, including asthma. The mainstay of therapy is gentle skin care and the application of topical steroids.
  • Contact dermatitis: local inflammation of the skin that is a result of direct contact with an irritant or allergen. The etiologies of contact dermatitis include allergic contact dermatitis (delayed type IV hypersensitivity reaction) or irritant dermatitis, which results from mechanical or chemical irritation of the skin. Lesions present with well-demarcated erythema and edema and may be pruritic or develop bullae with oozing. Treatment is with trigger avoidance and topical corticosteroids.
  • Psoriasis: multisystem inflammatory disease that includes skin findings. There are several subtypes of psoriasis. The most common subtype, chronic plaque psoriasis, presents with scaly, erythematous plaques that are intensely pruritic. These plaques most commonly affect extensor surfaces, which can distinguish it from other papulosquamous disorders. Treatment is focused on managing symptoms.
  • Scabies: local skin infection caused by the mite Sarcoptes scabiei. The clinical presentation of scabies usually includes small erythematous papules that are very pruritic and may have a linear distribution, which is evidence of mite movement underneath the skin. Common sites of infection are the extremities, classically the hands, and interdigital webs. Lesions may also appear as crusted, erythematous patches. Diagnosis is made clinically or with the detection of mites, eggs, or feces on microscopy of skin scrapings. Treatment is with topical permethrin.
  • Pityriasis rosea: skin disease that results in oval-shaped salmon-colored patches. An initial “herald” patch is followed by the emergence of multiple additional patches within 1–2 weeks after the initial patch. Pityriasis rosea may be associated with a prodrome of generalized malaise, headache, and pharyngitis. The disease course is typically mild and self-limited.
  • Seborrheic dermatitis: relapsing skin disorder that has an unclear pathogenesis and presents with yellow-tinged scales on well-demarcated, pruritic, erythematous plaques. These lesions are distributed in regions of the body with numerous sebaceous glands, including the scalp, face, and chest. Seborrheic dermatitis commonly presents as dandruff in adults and as “cradle cap” in infants. Some evidence suggests that Malassezia proliferation may be the etiology. Treatment includes topical antifungals and corticosteroids.
  • Subacute cutaneous lupus erythematosus (SCLE): form of skin lupus that is not usually associated with systemic lupus erythematosus (SLE). Subacute cutaneous lupus erythematosus presents with annular, erythematous, scaly plaques and usually appears on sun-exposed skin, including the neck, torso, and upper extremities. Counterintuitively, the face is usually spared. Subacute cutaneous lupus erythematosus can be drug-induced, with common offenders being antihypertensive agents, antihyperlipidemic agents, proton-pump inhibitors, antifungals, and tumor necrosis factor α inhibitors.
  • Granuloma annulare and erythema annulare centrifugum: benign, inflammatory conditions that present with annular, erythematous plaques. Granuloma annulare and erythema annulare centrifugum often do not have scales, which can be the factor distinguishing them from tinea infections.

References

  1. Mitchel TG. (2015). Medical mycology. In Brooks JE, et al. (Eds.), Jawetz, Melnick, & Adelberg’s Medical Microbiology, 27th ed. [VitalSource Bookshelf 9.4.3]. 
  2. Goldstein AO, Goldstein BG. (2021). Dermatophyte (tinea) infections. UpToDate. Retrieved April 29, 2021, from https://www.uptodate.com/contents/dermatophyte-tinea-infections
  3. Hawkins DM, Smidt, AC. (2014). Superficial fungal infections in children. Pediatric Clinics of North America 61:443–455. https://doi-org.online.uchc.edu/10.1016/j.pcl.2013.12.003
  4. Noble SL, Forbes RC, Stamm, PL. (1998). Diagnosis and management of common tinea infections. American Family Physician 58:163–178.
  5. Smith KJ, Neafie RC, Skelton HG, Barrett TL, Graham JF, Lupton GP.  (1991). Majocchi’s granuloma. Journal of Cutaneous Pathology 18:28. https://doi-org.online.uchc.edu/10.1111/j.1600-0560.1991.tb00598.x
  6. Merola JF. (2021). Overview of cutaneous lupus erythematosus. UpToDate. Retrieved May 1, 2021, from https://www.uptodate.com/contents/overview-of-cutaneous-lupus-erythematosus
  7. van Zuuren EJ, Fedorowicz Z, El-Gohary M. (2015). Evidence-based topical treatments for tinea cruris and tinea corporis: a summary of a Cochrane systematic review. British Journal of Dermatology 172:616–641. https://doi-org.online.uchc.edu/10.1111/bjd.13441
  8. Centers for Disease Control and Prevention. Ringworm. Retrieved May 2, 2021, from https://www.cdc.gov/fungal/diseases/ringworm/index.html

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