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:
- 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
- Direct contact with infected people or animals
- Indirect contact through a fomite
Host risk factors
- Walking barefoot in shared locker room
- Diabetes mellitus
- Copious sweating
- Occlusive footwear
- Contact with animals
- 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
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.
|Name||Body region||Etiology||Epidemiology and risk factors||Clinical features|
|Tinea pedis (“athlete’s foot”)||Feet, interdigital spaces of toes|
|Tinea corporis (“ringworm”)||Trunk and extremities (excluding hands and feet)|
|Tinea cruris (“jock itch”)||Groin, inguinal folds|
|Tinea unguium (onychomycosis)||Fingernails or toenails||T. rubrum|
|Tinea capitis||Hair follicles and scalp|
|Majocchi granuloma (fungal folliculitis)||Hair follicles on the body||T. rubrum|
Diagnosis and Management
- 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.
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
- 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.
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