Lesson
Read the Morphology and Protect the Diagnosis
Dermatophytes infect keratinized tissue, but site names do not prove an organism. Morphology, distribution, exposure, and a properly collected specimen turn pattern recognition into a defensible diagnosis.
- Keratin sites
- Active border
- KOH preparation
- Culture and molecular testing
- Tinea incognito
Name the infected compartment
Describe before treating
Match specimen to the question
Protect mimics and treatment-altered disease
Start with tissue and pattern
Inspect skin, hair, and nails separately. Record border activity, scale, central change, follicular involvement, alopecia, maceration, fissures, nail debris, distribution, symptoms, and treatment history.
Use testing when it changes care
Collect scale from an active edge for potassium hydroxide microscopy. Culture, histopathology, or molecular methods can answer organism, resistance, nail, hair, atypical, or treatment-failure questions. A negative poor specimen does not exclude disease.
Protect the differential
Nummular eczema, psoriasis, contact dermatitis, pityriasis rosea, erythrasma, candidiasis, bacterial infection, and other disorders can imitate tinea. Prominent scrotal involvement, absent scale, unusual pain, systemic illness, or failure should reopen the diagnosis.
Recognize treatment-altered disease
Corticosteroids can reduce redness and itch while fungus spreads. Ask about every cream, including combination products, and look for altered borders, atrophy, striae, pustules, or unexpectedly extensive disease.
Quick check
Lesson
Treat Body and Groin Disease as Connected Systems
Localized corporis and cruris often respond to topical therapy, but feet, nails, clothing, contacts, animals, and corticosteroid exposure can sustain recurrence.
- Tinea corporis
- Tinea cruris
- Topical boundary
- Reservoir sites
- Failure audit
Define extent and competing diagnoses
Continue beyond early symptom relief
Find autoinoculation reservoirs
Verify before escalating
Treat localized skin disease completely
Use an appropriate labeled topical antifungal over the lesion and beyond its visible edge for the full product-specific duration. Continue as directed even when itch and redness improve early.
Distinguish the groin differential
Tinea cruris often affects upper inner thighs and may spare the scrotum. Candidiasis, erythrasma, inverse psoriasis, irritant disease, and sexually associated emerging dermatophytes require different reasoning.
Find the reservoir
Inspect feet and nails, review household and animal exposure, launder contaminated clothing and towels, reduce shared items, and address moisture and friction. Autoinoculation can reseed treated skin.
Audit before escalating
Confirm diagnosis, product, amount, application boundary, frequency, duration, adherence, reinfection, follicular disease, host factors, and steroid exposure before changing therapy or assuming resistance.
Quick check
Lesson
Treat the Feet and Interrupt Recurrence
Interdigital, moccasin, and inflammatory patterns require attention to the whole foot, footwear, moisture, nails, barrier injury, and bacterial complications.
- Interdigital disease
- Moccasin scale
- Fissures
- Footwear
- Cellulitis risk
Choose therapy and vehicle
Reduce the fungal environment
Prevent bacterial entry
Separate cellulitis from tinea
Map the entire foot
Inspect between every toe, the sole, sides, heel, and nails. Maceration, diffuse scale, vesicles, odor, fissures, dystrophic nails, pain, and drainage change the differential and urgency.
Treat environment and skin
Dry carefully between toes, change socks, ventilate and rotate footwear, avoid sharing shoes or towels, and use sandals in communal wet areas. A powder may help moisture but does not replace therapeutic antifungal exposure when infection is present.
Protect high-risk feet
Diabetes, neuropathy, vascular disease, edema, immune compromise, and limited self-care increase harm from fissures and delayed infection. Avoid caustic self-treatment and arrange foot care when inspection or application is unsafe.
Escalate bacterial warning signs
Spreading redness, warmth, severe pain, pus, fever, lymphangitis, or systemic illness suggests bacterial complication. Fungal treatment alone is not adequate for cellulitis or an infected ulcer.
Quick check
Lesson
Separate Candida from Other Fold Disease
Intertrigo names inflammation in a fold. Candida is one cause, favored by moisture, friction, antibiotics, metabolic disease, immune compromise, and occlusion.
- Satellite pustules
- Moisture
- Erythrasma
- Inverse psoriasis
- Driver review
Support candidal disease
Do not equate fold rash with Candida
Treat the local environment
Review metabolic and immune drivers
Read candidal clues
A moist beefy erythematous fold eruption with peripheral satellite papules or pustules supports Candida, but testing can help when morphology, recurrence, or treatment response conflicts.
Keep competing diagnoses visible
Dermatophyte infection, erythrasma, bacterial intertrigo, inverse psoriasis, irritant friction, and allergic contact disease can overlap. Wood lamp examination, KOH, culture, distribution, and exposure history answer different questions.
Change the fold environment
Gently dry, reduce friction and occlusion, use breathable materials, manage incontinence or drainage, and create a sustainable skin-protection plan. Do not place absorbent material that remains wet against skin.
Investigate recurrence
Review glycemia, obesity, antibiotics, corticosteroids, immune status, and local anatomy when episodes are frequent, severe, or refractory. Recurrence can reveal a systemic or environmental driver.
Quick check
Lesson
Use Topical Antifungals as Drug Delivery Systems
Allylamines and azoles interrupt ergosterol biology at different enzymes. Active ingredient, organism, infected tissue, formulation, application boundary, and duration must align.
- Squalene epoxidase
- CYP51
- Vehicle
- Application technique
- Local reactions
Block squalene epoxidase
Block lanosterol demethylation
Move drug across the right surface
Make exposure executable
Map the pathways
Allylamines such as terbinafine inhibit squalene epoxidase. Azoles inhibit lanosterol 14 alpha demethylase, also called fungal CYP51. Both disrupt ergosterol biology through different targets.
Match spectrum and tissue
Dermatophyte and Candida likelihood, hair or nail involvement, lesion extent, inflammation, and prior exposure determine whether a topical drug is sufficient. Scalp follicle and nail matrix disease usually need a different exposure strategy.
Treat the vehicle as clinical
Creams fit many dry or mildly moist surfaces. Solutions, sprays, or gels can spread through hair or larger areas. Powders may reduce moisture. Choose around fissures, maceration, dexterity, stinging, coverage, and patient preference.
Write operational instructions
Specify clean and dry preparation, exact area, extension beyond the border, frequency, duration, missed-dose response, hand hygiene, adverse effects, and follow-up. Use teach-back rather than relying on a product name.
Quick check
Lesson
Treat Hair and Scalp Through the Follicle
Tinea capitis infects the hair shaft and follicle. Systemic therapy is required, while adjunctive shampoo and contact measures reduce transmission but do not replace oral treatment.
- Broken hairs
- Kerion
- Griseofulvin
- Systemic exposure
- Contact control
Identify the scalp pattern
Protect against scarring
Reach the infected follicle
Reduce shared exposure
Recognize the scalp patterns
Scale, alopecia, broken hairs, black dots, pruritus, lymph nodes, and inflammatory plaques can occur. A tender boggy kerion, drainage, pain, fever, or potential scarring needs prompt clinician assessment.
Use systemic therapy
Topical creams do not penetrate the infected hair shaft and follicle sufficiently. Oral griseofulvin, terbinafine, or another clinician-selected systemic antifungal depends on organism, age, formulation, safety, and local practice.
Dose griseofulvin by formulation
Microsize and ultramicrosize products are not milligram-for-milligram substitutes. Review weight, food-dependent absorption, liver disease, porphyria, lupus, reproductive risk, alcohol, warfarin, contraceptive reliability, and duration.
Control transmission
Adjunctive antifungal shampoo may reduce surface spores. Avoid shared combs, hats, bedding, clippers, and towels, identify symptomatic contacts and animal sources, and follow local school and public-health recommendations.
Quick check
Lesson
Confirm and Treat Nail Disease on the Nail Timeline
Onychomycosis is commonly mimicked by trauma, psoriasis, and other nail disorders. Confirm fungus, select therapy through extent and risk, and wait for healthy nail growth before judging appearance.
- Diagnostic confirmation
- Subungual debris
- Oral terbinafine
- Liver safety
- Nail growth
Exclude nonfungal dystrophy
Justify oral or topical therapy
Use systemic treatment safely
Separate slow growth from failure
Confirm before systemic treatment
Obtain a quality nail clipping or subungual specimen for KOH, culture, histopathology, or another suitable method. Sampling strategy depends on the nail pattern and prior antifungal exposure.
Choose through disease and patient
Number of nails, matrix involvement, thickness, pain, function, diabetes, circulation, immune status, liver disease, interactions, adherence, cost, and patient goals determine oral, topical, debridement, or referral strategy.
Use oral terbinafine safely
Current labeling uses 250 mg once daily for 6 weeks for fingernail and 12 weeks for toenail dermatophyte onychomycosis. Confirm disease, evaluate for chronic or active liver disease, obtain pretreatment transaminases, and follow current periodic assessment guidance.
Set the right response clock
Healthy nail grows slowly. Photograph or measure proximal clear growth and treat coexisting tinea pedis. Jaundice, dark urine, severe rash, taste or smell loss, depressive symptoms, or systemic illness requires prompt reassessment.
Quick check
Lesson
Investigate Failure and Emerging Resistance
Current CDC guidance highlights T indotineae and terbinafine-resistant T rubrum. Severe, extensive, atypical, or verified treatment-resistant disease may need specialized identification and susceptibility testing.
- T indotineae
- Resistant T rubrum
- TMVII
- Susceptibility testing
- Stewardship
Exclude ordinary failure
Consider emerging dermatophytes
Use specialized laboratories
Reduce pressure and delay
Audit common failure first
Reconfirm diagnosis, infected compartment, product, dose, duration, adherence, application, steroid exposure, reinfection, contacts, host factors, and specimen quality. Most failure mechanisms are not proven resistance.
Recognize emerging patterns
T indotineae can produce severe widespread inflammatory plaques and may resist terbinafine. TMVII can produce persistent genital, buttock, or facial lesions linked to intimate contact. Terbinafine-resistant T rubrum is also a concern.
Use the right laboratory
Routine laboratories may not distinguish T indotineae from related complexes. Culture, molecular identification, and antifungal susceptibility testing may require a reference laboratory and dermatology, infectious-disease, or public-health coordination.
Protect stewardship
Avoid unneeded steroid-antifungal combinations, incomplete treatment, serial ineffective courses, and unverified systemic exposure. Document treatment precisely and counsel contacts and hygiene without stigmatizing transmission.
Quick check
Lesson
Close the Loop Across Risk, Interaction, and Life Stage
Topical and systemic antifungal decisions change with age, pregnancy, lactation, liver disease, diabetes, circulation, immune status, drug interactions, access, and ability to complete treatment.
- Product-specific risk
- Pregnancy narrative
- Interaction review
- Teach-back
- Response targets
Treat neonatal and poorly examinable disease differently
Balance indication, evidence, and drainage reduction
Define a response window for every plan
Escalate whenever the pattern threatens vision
Use exact pediatric assessment and labeling
Do not stop after wax if impairment remains
Define a 48 to 72 hour checkpoint when infection is treated
Act on mastoid, neurologic, invasive, or sudden findings
Use age-specific labels and quantities
Reconcile every topical and systemic exposure
Do not rely on redness alone
Set targets, timing, and escalation
Individualize exposure
Name the actual systemic product
Confirm safe execution
Define the next decision
Prevent formulation errors
Use product-specific evidence
Hypersensitivity resolves slowly
Separate activity from recovery
Use narrative reproductive evidence
Do not use obsolete pregnancy letters. Review human and animal evidence, disease burden, route, exposure area, timing, alternatives, lactation, fertility, and shared goals for the exact product.
Reconcile systemic interactions
Azoles, terbinafine, and griseofulvin affect different enzymes and organ risks. Review prescription drugs, nonprescription products, supplements, alcohol, warfarin, CYP substrates, seizure therapy, contraception, hepatotoxic drugs, and QT risk when relevant.
Adapt to host risk
Children need weight and formulation checks. Diabetes, neuropathy, vascular disease, immune compromise, and liver disease change urgency and safety. Limited dexterity, vision, housing, laundry, or medication access can undermine an otherwise correct plan.
Define success and failure
Set a reassessment interval and track border activity, scale, itch, new lesions, hair or nail growth, contacts, adverse effects, adherence, and test results. State exactly when to stop treatment and seek help.
Quick check
Module test
Check the connections.
Each attempt draws 10 questions from the complete 112 question bank.
Each attempt draws a fresh set and rearranges the answer choices.
References
Current clinical foundation.
Lecture material was synthesized with the following contemporary guidance. Verify local policy and current guidance before applying clinical information.