Long case presentation: Tinea corporis

Cutaneous examination

• A raised, active, erythematous scaly peripheral border
• Fine scaling, most prominent at the advancing edge
• Central clearing or relative central hypopigmentation
• The margins may show small papules, vesicles, or pustules
• The lesions are associated with pruritus
• Distribution is usually asymmetrical; lesions may coalesce to form polycyclic plaques

Provisional diagnosis

Differential diagnoses

1. Nummular eczema
2. Pityriasis rosea
3. Psoriasis
4. Granuloma annulare
5. Erythema annulare centrifugum
6. Candidiasis, especially if lesions are in flexures

Investigations

• 10% potassium hydroxide (KOH) mount from skin scrapings taken from the active peripheral edge: shows branching, septate fungal hyphae.
• Fungal culture if diagnosis is uncertain, disease is recurrent/extensive, or there is poor response to treatment.
• Consider blood glucose testing in recurrent or extensive disease.

Final diagnosis

Very short practical description

There are multiple well-defined annular erythematous scaly plaques over the [site], with an active raised peripheral border and central clearing. The lesions are pruritic and show centrifugal extension. These findings are suggestive of tinea corporis. Diagnosis may be confirmed by a KOH mount of scrapings from the active edge showing septate branching hyphae.

KOH mount is more sensitive and gives a rapid result, whereas fungal culture is more specific, identifies the species, but takes weeks and can be falsely negative.

• Contamination during collection or in the laboratory
• Growth of a non-dermatophyte mould or yeast that is colonizing the specimen rather than causing the lesion
• The fungus may be present but not be the cause of the current clinical rash
• Misidentification of the isolate, especially with morphology-only identification

Fungal culture is considered the confirmatory test because it permits species identification, but it is slow and may be falsely negative. A positive culture must be correlated with KOH microscopy and clinical findings, as contamination or colonization can occur.

Common causes of a false-positive fungal culture

1. Environmental mould contamination during specimen collection, transport, or laboratory processing.
2. Inadequate cleaning of the site before sampling, especially nail and interdigital specimens.
3. Colonization rather than infection, particularly with Candida or non-dermatophyte moulds.
4. Sampling of dead keratin/debris that contains nonpathogenic fungi but not the actual pathogen.
5. Growth of a non-dermatophyte mould that is incidentally present, especially in nail samples.
6. Laboratory cross-contamination from another specimen or culture plate.
7. Misidentification based on colony morphology alone.
8. A true dermatophyte is cultured, but the current lesion has another diagnosis such as eczema or psoriasis.
9. Prior or partially treated infection where residual nonviable or colonizing fungi confuse clinical correlation.

A positive fungal culture should be interpreted with the clinical morphology and KOH microscopy. Repeated isolation of the same organism from a properly collected specimen supports pathogenic significance, especially for non-dermatophyte moulds.

Viva questions on tinea: current relevance in India

1. Why is dermatophytosis considered an important current problem in India?
   India has seen frequent chronic, recurrent, extensive, and treatment-refractory tinea corporis and tinea cruris, often associated with misuse of topical steroid combination creams and antifungal resistance.
2. Which dermatophyte is currently “talk of the town” in India?
   Trichophyton indotineae, an anthropophilic dermatophyte associated with widespread, recurrent, and often terbinafine-resistant infection.
3. What was T. indotineae previously called?
   It was previously reported within the Trichophyton mentagrophytes/interdigitale complex, especially as T. mentagrophytes ITS genotype VIII.
4. What clinical pattern should make you suspect T. indotineae infection?
   Extensive, highly pruritic, inflammatory tinea corporis, tinea cruris, or tinea faciei with large annular or polycyclic plaques, recurrence, family involvement, and poor response to standard terbinafine treatment.
5. Why is T. indotineae important?
   It has high rates of terbinafine resistance, making formerly routine treatment less reliable. Recent reviews describe major diagnostic and therapeutic challenges associated with this organism, including in India. Recent clinical update
6. What is the molecular mechanism of terbinafine resistance?
   Mutations in the squalene epoxidase (SQLE) gene reduce susceptibility to terbinafine, which inhibits this enzyme in ergosterol synthesis.
7. Which topical preparations have worsened the tinea epidemic in India?
   Irrational fixed-dose combinations containing a potent corticosteroid plus antifungal, often with an antibacterial agent, for example clobetasol plus antifungal plus antibiotic combinations.
8. Why are topical steroids harmful in tinea?
   Steroids suppress local inflammation and alter the lesion, producing temporary symptomatic relief but allowing fungal proliferation, extensive disease, atypical morphology, recurrence, and treatment failure.
9. What is tinea incognito?
   Dermatophytosis whose typical appearance has been modified by topical or systemic corticosteroids or other immunosuppressive therapy. It becomes less scaly, less sharply marginated, more extensive, and may show pustules.
10. What are the common adverse effects of steroid-containing creams used for tinea?
    Skin atrophy, striae, telangiectasia, hypopigmentation, acneiform eruption, secondary bacterial infection, tinea incognito, and persistence or spread of fungal infection.
11. What are the major reasons for recurrent tinea in India?
    Incomplete treatment, poor adherence, self-medication, topical steroid misuse, reinfection from close contacts, untreated tinea pedis or onychomycosis, infected clothing or fomites, humid climate, and resistant dermatophytes.
12. Why should family members be examined in recurrent tinea?
    Dermatophytes spread through close skin-to-skin contact and shared towels, clothing, bedding, and grooming items. An untreated household contact can cause reinfection.
13. What advice do you give regarding fomites and hygiene?
    Avoid sharing clothes, towels, bedsheets, and footwear; wash clothes and linen regularly; dry them thoroughly; wear loose cotton garments; keep skin folds dry; and treat infected household contacts where appropriate.
14. What is the proper site for collecting a KOH specimen in tinea corporis?
    Scrape the active, advancing scaly peripheral edge of an untreated lesion, not the central healed area.
15. What does a KOH mount show in dermatophytosis?
    Branching, septate hyphae in skin scales. It is rapid and useful at the bedside but does not identify the species or distinguish viable from nonviable fungi.
16. When should fungal culture and species identification be considered?
    In recurrent, extensive, atypical, steroid-modified, chronic, or treatment-resistant disease, and when a resistant organism such as T. indotineae is suspected.
17. Why may a fungal culture be negative despite true tinea?
    Prior antifungal use, inadequate sample, sampling from the wrong site, insufficient viable fungus, improper transport, or poor laboratory growth conditions.
18. Is a positive fungal culture always proof that the cultured fungus is causing the lesion?
    No. Correlate it with morphology and KOH microscopy. Contamination, colonization, and incidental non-dermatophyte moulds may occur.
19. What is the difference between chronic and recurrent dermatophytosis?
    • Chronic dermatophytosis: infection persists continuously for a prolonged duration despite treatment.
    • Recurrent dermatophytosis: lesions clear clinically but reappear after an interval.
20. What is the key public-health message for tinea in India?
    Tinea is not merely a cosmetic complaint. Appropriate diagnosis, avoidance of steroid-containing combination creams, adherence to a complete antifungal course, treatment of reservoirs and contacts, and rational antifungal use are needed to limit chronicity and antifungal resistance.

One high-yield closing line for viva

In India, the major current concern in dermatophytosis is chronic and recalcitrant tinea associated with topical corticosteroid misuse and the emergence of terbinafine-resistant Trichophyton indotineae.

Tinea imbricata vs tinea pseudoimbricata

Tinea imbricata

There are multiple well-defined, extensive, concentric, annular scaly plaques with overlapping, imbricated scales. The lesions show minimal inflammation and little or no vesiculation. The morphology is suggestive of tinea imbricata.

Tinea pseudoimbricata

There are multiple erythematous annular and polycyclic plaques with concentric active scaly borders, producing a ring-within-a-ring appearance. There may be pruritus, peripheral papules, vesicles, or pustules. In a patient with use of steroid-containing combination creams, this is suggestive of tinea pseudoimbricata.

India-specific significance

One-line viva answer

Tinea imbricata is true imbricated dermatophytosis caused by Trichophyton concentricum, whereas tinea pseudoimbricata is an imbricata-like, ring-within-a-ring pattern caused by other dermatophytes, usually after topical steroid misuse or in an immunocompromised patient.