Tinea pedis, tinea cruris and tinea unguium — SAQ

Stem

A 34-year-old man presents with a 6-week history of itchy, scaly rash in both groins. The rash is sharply marginated, erythematous and scaly, with central clearing. On examination the scrotum and penis are spared. Both feet show maceration and scaling between the 4th and 5th toes, and both great toenails are thickened, yellow-brown and dystrophic with subungual debris. He is otherwise well.

Questions

a) What is the most likely diagnosis and what clinical features support it? (2 marks)

b) What investigations would you arrange to confirm the diagnosis? (3 marks)

c) Outline your management plan for this patient. (3 marks)

d) What are the key complications and prognostic factors? (2 marks)

Model answer (must-hit points)

^[3]a) Diagnosis and supporting features (2 marks)

• Tinea cruris with coexisting tinea pedis and tinea unguium/onychomycosis — 1 mark.
• Key features: sharply marginated, scaly, groin rash with central clearing and scrotal sparing (unlike candidiasis); coexisting interdigital maceration and scaling; thickened, discoloured, dystrophic toenails with subungual debris — 1 mark.

^[2][3]b) Investigations (3 marks)

• KOH microscopy of skin scrapings from the groin and toe webs, and of subungual debris — branching septate hyphae confirm dermatophyte infection — 1 mark.
• Fungal culture with species identification, especially if disease is extensive, refractory or T. indotineae is suspected; nail culture takes 2–6 weeks — 1 mark.
• PAS stain of nail clippings as the most sensitive single test for onychomycosis; consider it before committing to long systemic therapy — 1 mark.

^[2]c) Management (3 marks)

• Skin disease: topical allylamine (terbinafine 1%) or azole applied to groin and feet for 1–4 weeks; continue 1 week beyond clinical clearance; treat the foot reservoir to prevent groin relapse — 1 mark.
• Nail disease: oral terbinafine 250 mg daily for 12 weeks (toenails) or 6 weeks (fingernails); baseline and monitoring liver function; alternative is itraconazole if terbinafine contraindicated or T. indotineae suspected — 1 mark.
• Adjunctive measures and prevention: keep feet dry, change socks daily, wear breathable footwear, rotate shoes, avoid walking barefoot, do not share towels or nail clippers, consider podiatric debridement of thickened nails — 1 mark.

^[1]d) Complications and prognosis (2 marks)

• Complications: secondary bacterial infection, cellulitis, lymphangitis, recurrent lower-limb cellulitis (especially in diabetes), tinea incognito from steroid use, dermatophytid reaction — 1 mark.
• Prognosis: skin disease usually responds well; onychomycosis has a slower response and recurrence of 20–50% because the nail is a protected reservoir; cure requires the nail to grow out, which takes 12–18 months for toenails — 1 mark.

References3ShowHide

1. [1]Lipner SR, Scher RK. Onychomycosis: Treatment and prevention of recurrence J Am Acad Dermatol, 2019.PMID 29959962
2. [2]Gupta AK, Polla Ravi S, Talukder M, et al. Effectiveness and safety of oral terbinafine for dermatophyte distal subungual onychomycosis Expert Opin Pharmacother, 2024.PMID 38221907
3. [3]Leung AK, Barankin B, Lam JM, et al. Tinea pedis: an updated review Drugs Context, 2023.PMID 37415917