Dermatology & Allergy · Full case
Fungal Infections
Superficial Fungal Infections · Clinical Reasoning Framework v2
GP & SCA · NICE CKS · Tinea (corporis/pedis/cruris/capitis/unguium) · candida · pityriasis versicolor · confirm before oral antifungals · the underlying-cause clue
Tinea = the ring with a scaly edgeDermatophyte (tinea) infections classically form an annular, scaly, itchy plaque with central clearing and a raised advancing edge. Site names the type: corporis (body), pedis (foot/athlete's foot), cruris (groin), capitis (scalp), unguium (nail). Topical antifungals are first-line for most skin tinea
Confirm nails & scalp before oral treatmentOral antifungals (terbinafine, itraconazole, griseofulvin) carry side effects/monitoring — so confirm the diagnosis with nail clippings / skin scrapings / hair samples for microscopy & culture before committing to weeks–months of oral therapy for onychomycosis or tinea capitis. Don't treat a dystrophic nail blindly
Tinea capitis = oral + don't miss kerionScalp ringworm needs ORAL antifungals (topical won't penetrate the hair follicle) — confirm with samples, treat household contacts/fomites, and recognise a kerion (boggy, inflamed, pustular scalp mass) which needs prompt treatment to prevent scarring alopecia. Common in children
Steroid-modified tinea (tinea incognito)Topical steroids applied to an unrecognised tinea blur the picture — less scaly, more extensive, atypical. If a "dermatitis" worsens or spreads on steroids, think tinea: stop the steroid, scrape and treat as fungal. A classic misdiagnosis
Candida loves warm, moist, immunosuppressedCandidal intertrigo (skin folds), oral thrush, vulvovaginal and balanitis favour moisture, occlusion, antibiotics, pregnancy, and immunosuppression. Recurrent/severe/oral candida in an adult should prompt a search for diabetes or immunosuppression (incl. HIV)
Look for the underlying causeRecurrent or widespread fungal infection is a clue: undiagnosed DIABETES (check HbA1c), immunosuppression/HIV, steroid/antibiotic use, athlete's foot as the source of recurrent cellulitis, or an animal source for tinea. Treat the predisposing factor, not just the rash
Athlete's foot → cellulitis portalTinea pedis (especially macerated toe-web) is a common entry point for bacterial cellulitis of the leg, particularly in those with oedema/diabetes — treating the fungal infection and skin care reduces recurrent cellulitis. Don't overlook the feet
It's often NOT fungalMimics abound: eczema/psoriasis (incl. flexural & scalp), discoid eczema, granuloma annulare, erythrasma (coral-red on Wood's light), seborrhoeic dermatitis, and — crucially — never dismiss a changing/ulcerating lesion as "fungal" without considering skin cancer. Confirm if unsure
📋 Clinical Stem — Fungal Infections
A 56-year-old man with months of thickened, discoloured toenails and an itchy, scaly foot rash, who has tried steroid cream that made it worse, and asks for "the tablets to clear my nails"
Gary Pollard, 56, attends wanting "those tablets" to clear several thickened, yellow, crumbly toenails he's had for over a year, which embarrass him. He also has an itchy, scaly, peeling rash between his toes and on the sole, and a faint scaly ring on his groin. He used a steroid cream from a pharmacy on the groin patch, which initially soothed it but it then spread and became less obviously ring-shaped. He has put on weight, feels thirsty and tired lately, and his father had diabetes. He hopes to leave with a prescription for oral antifungal tablets today.
This stem tests the ability to: recognise the spectrum of superficial fungal infection (onychomycosis, tinea pedis, tinea cruris) and the classic clues (annular scaly edge, central clearing); to recognise STEROID-MODIFIED tinea (tinea incognito) from the history of a steroid cream making a "ring" worse and atypical; to insist on CONFIRMING nail/skin samples (microscopy & culture) before committing to oral antifungals (terbinafine) given their side effects/monitoring — rather than prescribing blindly on request; to search for the UNDERLYING CAUSE (this man has symptoms of undiagnosed diabetes — polyuria/thirst/weight change, fatigue, family history — check HbA1c), and to recognise athlete's foot as a portal for cellulitis; and to advise on hygiene/recurrence and topical-first treatment. The SCA challenge is to manage the request for oral tablets responsibly (confirm first), while diagnosing the bigger picture (likely diabetes) behind recurrent fungal disease.
Scenario A — Onychomycosis + tinea + underlying diabetes (this stem) Confirm nail samples before oral terbinafine; recognise steroid-modified tinea; check HbA1c (undiagnosed diabetes); treat tinea pedis/cruris topically; hygiene/recurrence advice.
Scenario B — Tinea corporis/cruris/pedis Annular scaly plaques; topical antifungal (terbinafine/imidazole) first-line; treat the feet (source); hygiene; avoid steroid monotherapy.
Scenario C — Tinea capitis / kerion (child) Scalp scaling/hair loss → samples + ORAL antifungal; treat contacts/fomites; kerion (boggy inflamed mass) → prompt treatment to avoid scarring.
Scenario D — Candida (intertrigo/oral/genital) Moist folds, oral thrush, vulvovaginal/balanitis; topical/oral azole; in recurrent/oral adult candida search for diabetes/immunosuppression (HIV).
Scenario E — The mimic / red flag Eczema/psoriasis, erythrasma (coral-red on Wood's light), seborrhoeic dermatitis, or a changing/ulcerating lesion that could be skin cancer — confirm; don't label "fungal" reflexively.
Key variables to adapt for Type/site of infection; confirm before oral antifungals (nails/scalp); steroid-modified tinea; underlying cause (diabetes/immunosuppression/HIV); athlete's foot → cellulitis; candida triggers; tinea capitis = oral + contacts; mimics & skin-cancer caution; drug interactions/monitoring with oral antifungals.
Steps:
1
Step 1
History — The Lesions · Steroid-Modified Clue · Underlying Cause · ICE
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The history characterises the lesions (site, appearance, itch, duration), pulls out the steroid-modified clue (a "ring" made worse by steroid cream), and — crucially — looks beyond the rash for an underlying cause, because recurrent or widespread fungal infection is often a flag for diabetes or immunosuppression. Gary's request for "the tablets" is reasonable but must be earned by confirmation, and his thirst/weight change/fatigue are the bigger diagnosis hiding in plain sight.
🎓 SCA framing — confirm before tablets; look for the cause
"I can absolutely help with the nails — but the tablets for that need taking for months and can affect the liver, so before we commit, I'll take a nail sample to confirm it's a fungus. And a few things you've mentioned make me want to check for a reason these keep coming back."
The skill is to honour his goal (clear nails) while explaining why confirmation comes first, and to widen the lens to the likely underlying diabetes — turning a "prescription request" into a properly worked-up consultation.
1A — Lesions, modifiers and underlying cause
1B — Red flags / things not to miss
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Red Flags — beyond the simple ringworm
| Red flag | Why it matters | Action |
|---|---|---|
| Recurrent/widespread fungal infection — undiagnosed diabetes or immunosuppression/HIV | The fungal infection is a symptom of a treatable systemic condition. | Check HbA1c; consider immunosuppression/HIV testing; treat the cause |
| Steroid-modified tinea (tinea incognito) | Misdiagnosis perpetuates and worsens infection. | Stop steroid; skin scrapings; treat as fungal |
| Tinea capitis / kerion | Scarring alopecia if untreated; needs oral therapy & contact treatment. | Hair/scalp samples + oral antifungal; treat contacts; prompt treatment of kerion |
| Athlete's foot as a portal for cellulitis | Recurrent leg cellulitis, especially with oedema/diabetes. | Treat tinea pedis; foot/skin care; treat cellulitis if present |
| Changing / ulcerating / non-healing "fungal" lesion | Skin cancer or alternative diagnosis mislabelled as fungal. | Reconsider diagnosis; dermatology referral/biopsy; don't treat blindly |
| Before oral antifungals — drug interactions / hepatotoxicity | Terbinafine/itraconazole carry interactions and liver risk. | Confirm diagnosis; review interactions; baseline/monitor LFTs per guidance |
1C — ICE
💭 Ideas
"What do you think is going on with the nails and skin — and what were you hoping for today?"
Gary believes it's "just fungus" and wants tablets. Surfacing this lets you agree it's likely fungal AND explain why confirmation comes first, and gently introduce that you'd like to check why it keeps recurring — so the wider work-up feels logical, not obstructive.
😟 Concerns
"Is it the appearance that bothers you most, or something else?"
His concern is embarrassment about the nails. Acknowledging it validates the request; it also opens the door to the fatigue/thirst he's downplayed, which is the more important issue.
🎯 Expectations
"You're hoping for the tablets — let me explain how we get you there safely."
Naming the expectation lets you set out the plan: confirm with a nail sample, check a few bloods (including for diabetes), then start oral treatment if confirmed and safe — so he leaves with a clear route rather than disappointment.
1D — Psychosocial context
🔬 Why confirm first
Explain the rationale for sampling before oral tablets.
"The nail tablets work, but they're a long course and can affect the liver, so it's worth a quick nail clipping to be sure it's a fungus first — about half of dodgy-looking nails turn out not to be."🩸 The diabetes conversation
Connect recurrence to the bigger picture sensitively.
"These infections sometimes keep coming back when blood sugar's running high — and with the thirst and tiredness you've mentioned, I'd really like to check for diabetes. Sorting that out would help your skin too."🦶 Treat the source
Explain athlete's foot feeding the rest.
"The athlete's foot is likely the source that's spread to your groin and nails — so treating your feet properly, keeping them dry, and not sharing towels stops it coming back."🚫 Undoing the steroid
Explain why the steroid cream made it worse.
"That steroid cream calmed the itch but actually fed the fungus and spread it — so we'll stop it and use an antifungal instead."🎓 SCA Checkpoint — Step 1TasksRelating to OthersGlobal Skills
Key phrases that score
"Before months of tablets, I'll take a nail clipping to confirm it's fungal." — confirm before orals.
"The thirst, tiredness and recurrences make me want to check for diabetes." — finds the cause.
"The steroid cream made the ring spread — that points to a fungus." — recognises tinea incognito.
Deductions
- Prescribing oral antifungals for nails without confirmation
- Missing the underlying diabetes/immunosuppression
- Not recognising steroid-modified tinea
- Treating the rash but not the source (feet)/hygiene
🔴 Red
Oral antifungal for nails on request, unconfirmed; diabetes missed; steroid-modified tinea unrecognised; no source/hygiene
🟠 Amber
Diagnoses tinea; treats topically; mentions confirming nails; underlying cause partly considered; ICE partial
🟢 Green
Confirms nails before orals; recognises tinea incognito; checks HbA1c/underlying cause; treats source + hygiene; ICE all three; safety-net
2
Step 2
Triage — Urgent (Cellulitis/Kerion/Immunosuppressed) · Confirm-then-Treat · Routine Topical
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Most fungal infection is routine and topical. Triage pulls out the complications and special situations — cellulitis, kerion, the immunosuppressed, and the changing lesion that isn't fungal — and routes nail/scalp disease through "confirm then oral".
🔴 Urgent
Soon / same day
Don't delay- Cellulitis (from tinea pedis)Treat infection; manage the fungal portal
- Kerion / extensive tinea capitisPrompt oral treatment; avoid scarring
- Immunosuppressed / severe / unwellInvestigate; consider specialist
🟠 Confirm → treat
Sample first
Before orals- OnychomycosisNail clippings → terbinafine if confirmed
- Tinea capitisHair/scalp samples → oral + contacts
- Diagnostic doubt / treatment failureScrapings; reconsider mimic
🟢 Routine
Topical
First-line- Tinea corporis/cruris/pedisTopical antifungal + hygiene
- Candidal intertrigo / genitalTopical/oral azole; address moisture
- Pityriasis versicolorTopical antifungal; counsel re pigment
🎓 SCA Checkpoint — Step 2Tasks
Triage rationale
"Your skin tinea we can treat with creams straight away; for the nails, the right step is to confirm with a clipping before starting tablets — and meanwhile I'll check why this keeps happening."
Deductions
- Starting orals without confirmation
- Missing cellulitis/kerion/immunosuppression
3
Step 3
Examination — Morphology & Distribution · Feet/Nails/Folds · Wood's Light
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Examination characterises the morphology (annular, scaly advancing edge, central clearing), maps the distribution (feet, web spaces, nails, groin, folds, scalp), and uses simple aids (Wood's light) to support the diagnosis and separate the mimics.
🎓 SCA Checkpoint — Step 3TasksGlobal Skills
Narration that scores
"I'll look at the rash's shape and edge, check your feet and the web spaces between your toes, examine the nails, and look in the skin folds — and I'd like to take a nail clipping and a skin scraping to confirm."
Deductions
- Not examining the feet (source) when treating groin/nails
- Mislabelling eczema/psoriasis/erythrasma as tinea
4
Step 4
Investigations — Confirm (Microscopy & Culture) · HbA1c · Underlying Cause
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Simple skin tinea can be treated topically without tests; nail and scalp disease should be confirmed (microscopy & culture) before oral antifungals; and recurrent/widespread disease warrants a search for an underlying cause — most importantly HbA1c for diabetes.
💬 "Why not just start the tablets today?"
"I want to get you on them — but the nail tablets are a long course and occasionally affect the liver, and not every odd-looking nail is actually fungal. A quick clipping confirms it, so we don't put you through months of medication for nothing. And while we wait, I'll check a blood test for diabetes, because that's often why these infections keep coming back — sorting it would help your skin and your health overall."
🎓 SCA Checkpoint — Step 4Tasks
Key reasoning
"I'll send a nail clipping to confirm the fungus, check an HbA1c for diabetes, and a baseline liver test — then if it's confirmed we'll start the tablets safely."
Deductions
- Oral antifungals without confirmation/LFTs/interaction check
- Not checking HbA1c in recurrent fungal disease with diabetic symptoms
5
Step 5
Diagnosis — Type/Site · Steroid-Modified · The Mimics · The Cause
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Name the fungal diagnosis by type/site, flag steroid modification, separate the mimics, and — the higher-order step — name the underlying cause driving recurrence.
🚩 Treat the rash, find the cause, confirm the orals
Gary's formulation is multi-site dermatophyte infection (tinea pedis spreading to cruris and nails) with steroid-modification of the groin lesion, very likely on a background of undiagnosed diabetes (thirst, weight change, fatigue, family history). The plan: confirm the nails before oral terbinafine, stop the steroid and treat as fungal, treat the feet as the source with hygiene advice, and check HbA1c — treating the person and the cause, not just the visible rash.
🎓 SCA Checkpoint — Step 5Tasks
Explaining it plainly
"This is a fungal infection that's spread from your feet to your groin and nails. The steroid cream made the groin patch worse. I'll confirm the nails before starting tablets, treat the skin with creams, and check for diabetes — which is probably why it keeps coming back."
Deductions
- Naming the rash without seeking the underlying cause
- Missing steroid-modified tinea / a mimic
6
Step 6
Referral — Dermatology · Diabetes Pathway · Specialist Situations
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Most fungal infection is managed in primary care. Referral is for diagnostic uncertainty/treatment failure, extensive/resistant or immunosuppression-related disease, severe tinea capitis/kerion, and the suspicious lesion that may not be fungal — plus onward management of any newly-found diabetes.
🎓 SCA Checkpoint — Step 6Tasks
Right onward care
"Most of this we'll manage here. If the HbA1c shows diabetes we'll start you on that pathway, and if any lesion looked unusual or didn't settle I'd involve dermatology."
Deductions
- Not acting on newly-found diabetes
- Not referring a non-resolving/suspicious lesion
7
Step 7
Management — Topical First · Oral (Confirmed) · Treat the Cause · Hygiene/Recurrence
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Management is topical antifungals for most skin tinea/candida, oral antifungals (after confirmation) for nails and scalp, treatment of the source and predisposing factors (diabetes, moisture, steroids), and hygiene advice to prevent recurrence.
🎓 SCA Checkpoint — Step 7TasksRelating to OthersGlobal Skills
A plan that scores
"Here's the plan: antifungal cream for the skin and feet, stop the steroid, and a nail clipping plus blood tests today — including for diabetes. If the nail sample confirms fungus and your liver test is fine, we'll start the tablets. Keep your feet dry, don't share towels, and come back if it spreads or your leg gets hot and red."
Deductions
- Oral antifungal without confirmation/safety checks
- Treating the rash but ignoring diabetes/source/hygiene
- Continuing steroid monotherapy
Fungal Infections — SCA Consultation Scorecard
Diagnose tinea/candida · confirm before orals · steroid-modified · find the cause (diabetes) · hygiene
0/ 33 pts
Global Skills
Structure, language, responsiveness
0/7
Tasks
Clinical reasoning, diagnosis, management
0/15
Relating to Others
Communication, rapport, shared decisions
0/11
RAG Self-Assessment
🔴 Red
Oral antifungal on request, unconfirmed; diabetes missed; steroid-modified tinea unrecognised; no source/hygiene; no safety-net
🟠 Amber
Diagnoses tinea; topical treatment; confirms nails; underlying cause partly considered; hygiene/source partial; ICE partial
🟢 Green
Diagnoses by site; confirms nails before orals (LFTs/interactions); checks HbA1c; recognises tinea incognito; treats source + hygiene; ICE all three; safety-net
Complete the checklist to see your score and feedback
"Doc, my toenails have gone thick and yellow and crumbly — they're embarrassing, I've had them over a year. I read you can get tablets that clear them. Can I just get a prescription for those?"
Who you are
Gary Pollard, 56. Several thickened, yellow, crumbly toenails for over a year — you find them embarrassing and want "the tablets" to clear them. You also have an itchy, scaly, peeling rash between your toes and on the sole, and a faint scaly ring in your groin. You used a steroid cream from the pharmacy on the groin, which soothed it at first but then it spread and lost its ring shape. Lately you've put on weight, feel thirsty and tired, and your dad had diabetes. You're hoping to walk out with a prescription for antifungal tablets.
Hidden concerns (reveal if explored)
Embarrassment (main): the nails bother you cosmetically; you want them sorted.
Downplayed symptoms: you'll mention the thirst, tiredness and weight gain only if asked — you hadn't connected them to anything.
Impatience: you just want the tablets and may be mildly resistant to "more tests".
Clinical details if asked
- Onychomycosis (several toenails, >1 year); tinea pedis (itchy, scaly, peeling between toes/sole); tinea cruris (groin ring)
- Used a topical steroid on the groin → spread and became atypical
- Recent weight gain, thirst, polyuria, fatigue; father had type 2 diabetes
- No hot/red/swollen leg (no current cellulitis); no changing/ulcerating lesions
- On no regular medication; happy to have a nail clipping and blood tests
Reactions at key moments
- If the doctor just prescribes oral antifungals: you're pleased — so a strong candidate must confirm first and explain why.
- On "let's confirm with a nail clipping": mildly impatient, accepting when the reasons (long course, liver) are explained.
- On the diabetes check: surprised but take it seriously given your dad.
- On the steroid having made it worse: "Oh — I thought it was helping."
- Challenge line: "Can't you just give me the tablets now and skip all the tests?"
"I really just want the tablets to clear my nails — can't you prescribe them today and skip all the swabs and blood tests?"
Resolution: Gary is well served if the GP: (1) recognises the multi-site dermatophyte infection (tinea pedis/cruris/onychomycosis) and the steroid-modified groin lesion; (2) confirms the nails (clippings, microscopy & culture) with baseline LFTs/interaction check before committing to oral terbinafine, explaining why; (3) searches for the underlying cause and checks HbA1c given his thirst/weight/fatigue/family history (likely undiagnosed diabetes); (4) treats the skin topically, stops the steroid, treats the feet as the source, and gives hygiene/recurrence advice; (5) safety-nets and arranges follow-up. He is poorly served if simply handed oral antifungals without confirmation or any search for the cause.
Clinic Quick Reference
Fungal Infections — Clinical Decision Framework
Tinea/candida · confirm before orals · find the cause
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🔍 1 — Diagnose
Tinea: annular, scaly advancing edge, central clearing — corporis/cruris/pedis/capitis/unguium. Candida: moist folds/mucosa, satellite pustules. Pityriasis versicolor: pigmented scaly macules. Steroid-modified tinea: atypical/spreading on steroid → stop steroid, scrape, treat as fungal. Confirm nails/scalp (microscopy & culture) before oral antifungals.
💊 2 — Treat & look deeper
Topical first for skin tinea/candida; oral (terbinafine/itraconazole, confirmed, LFTs/interactions) for nails; tinea capitis = oral + treat contacts (kerion promptly). Treat the source (feet) & hygiene; athlete's foot is a cellulitis portal. Find the cause: recurrent/widespread → HbA1c (diabetes), consider immunosuppression/HIV. Don't label a changing/ulcerating lesion "fungal" — consider skin cancer.
SCA Quick Reference
Fungal Infections — Consultation Playbook
Confirm before orals · find the cause · treat the source
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🎯 The three pivots that pass this case
1 · Confirm before orals
Nail/scalp disease → microscopy & culture before oral antifungals (side effects, monitoring, interactions).
2 · Find the cause
Recurrent/widespread fungal infection → check HbA1c (diabetes); consider immunosuppression/HIV; stop steroids.
3 · Treat the source
Treat tinea pedis (the source & cellulitis portal) + hygiene; topical-first for skin; capitis = oral + contacts.
⛔ Don't start oral antifungals for nails/scalp without confirming (samples, LFTs, interactions) · Don't miss the underlying diabetes/immunosuppression behind recurrence · Don't miss steroid-modified tinea · Don't forget the feet (source) and hygiene · Don't label a changing/ulcerating lesion "fungal" — consider skin cancer