About This Page
This is a clinician-written, evidence-based guide aligned to the MCC Examination Objectives. It is structured by clinical presentation — the way the MCCQE tests and the way patients actually present. Management reflects current Canadian guidelines (CMA, CFPC, CPS). Always cross-reference with institutional protocols and clinical judgment.
The Bottom Line
- Single-nail longitudinal melanonychia with widening, irregular pigment, nail-fold extension, or adult onset is subungual melanoma until assessed
- Confirm onychomycosis before systemic antifungals; Choosing Wisely Canada cautions against systemic antifungal use without mycological confirmation
- Clubbing is not a cosmetic nail problem: assess lung cancer, chronic lung disease, cyanotic heart disease, endocarditis, and inflammatory bowel/liver disease
- Acute paronychia is usually bacterial and drainage is needed if abscess is present; chronic paronychia is usually irritant/wet-work related
- Nail findings often provide systemic clues: pitting in psoriasis/alopecia areata, koilonychia in iron deficiency, splinter haemorrhages in endocarditis/trauma, Beau lines after systemic illness
Approach to the Presentation
Nail complaints should be approached by the number of nails involved, tempo, pain, trauma, occupational wet work, cosmetic exposures, associated skin disease, systemic symptoms, and pigment pattern. Examine all fingernails and toenails, periungual skin, scalp, skin plaques, mucosa, joints, and signs of systemic disease. A painful swollen nail fold is different from thickened yellow nails, a pitted nail, or a single pigmented longitudinal band. The MCCQE1 pattern is to avoid reflexively diagnosing fungus: confirm fungal disease before systemic treatment, identify red flags for melanoma, and recognize systemic nail signs.
Differential Diagnosis
| diagnosis | likelihood | key features | distinguishing test |
|---|---|---|---|
| Subungual Melanoma | must-not-miss | Single-nail longitudinal melanonychia, widening or irregular band, variegated colour, nail dystrophy, Hutchinson sign, adult onset, thumb/great toe | Urgent dermatology referral and nail-matrix biopsy |
| Digital Clubbing from Systemic Disease | must-not-miss | Bulbous distal digits, loss of Lovibond angle, spongy nail bed; associated lung cancer, bronchiectasis, cystic fibrosis, cyanotic heart disease, endocarditis, IBD, cirrhosis | Clinical recognition; CXR and targeted cardiopulmonary/GI evaluation based on symptoms |
| Infective Endocarditis Signs | must-not-miss | Splinter haemorrhages with fever, murmur, risk factors, embolic signs, Janeway lesions, Osler nodes; nail finding alone is nonspecific | Blood cultures and echocardiography when clinical suspicion exists |
| Felon / Deep Space Infection / Herpetic Whitlow | must-not-miss | Severe fingertip pain, tense pulp swelling, vesicles in whitlow, immunocompromise, occupational exposure; wrong incision can worsen whitlow | Clinical diagnosis; HSV PCR if vesicular/unclear; avoid incision for herpetic whitlow |
| Onychomycosis | common | Thickened yellow-white brittle nail, subungual debris, onycholysis, tinea pedis; toenails more common | KOH, fungal culture, PAS stain, or PCR before oral antifungal therapy |
| Psoriatic Nail Disease | common | Pitting, oil-drop/salmon patch, onycholysis, subungual hyperkeratosis; psoriasis plaques or psoriatic arthritis symptoms | Clinical diagnosis; examine skin, scalp, joints; fungal test if uncertain |
| Acute Paronychia | common | Painful erythematous swollen nail fold, often after hangnail, biting, manicure, trauma; abscess may be visible | Clinical diagnosis; culture if recurrent, severe, immunocompromised, or treatment failure |
| Chronic Paronychia | common | Chronic swollen nail folds, absent cuticle, nail ridging; wet work, irritants, detergents; Candida may colonize but inflammation is often irritant | Clinical diagnosis; occupational exposure history |
| Ingrown Toenail | common | Painful lateral nail fold inflammation, granulation tissue, often great toe; tight footwear or improper trimming | Clinical diagnosis; assess infection and recurrence |
| Koilonychia / Iron Deficiency | less common | Spoon-shaped nails with fatigue, pallor, pica, heavy menstrual bleeding, GI blood loss, vegetarian/low iron intake | CBC and ferritin; evaluate cause of iron deficiency |
| Beau Lines / Onychomadesis | less common | Transverse grooves or nail shedding after severe systemic illness, fever, chemotherapy, trauma, hand-foot-mouth disease | Clinical timeline; grows out with nail plate |
| Yellow Nail Syndrome | rare | Slow-growing yellow thickened nails with lymphoedema, chronic sinusitis, bronchiectasis, or pleural effusion | Clinical features plus chest imaging and respiratory assessment |
Red Flags & Key History
Symptoms
New or changing single-nail pigment band in an adult, especially widening or irregular
Pigment extending onto proximal or lateral nail fold (Hutchinson sign)
Fever, murmur, embolic symptoms, injection drug use, prosthetic valve, or recent bacteraemia with splinter haemorrhages
New clubbing with cough, haemoptysis, dyspnea, weight loss, cyanosis, or GI symptoms
Severe throbbing fingertip pain, immunosuppression, diabetes, or spreading cellulitis
Wet work, gloves, detergents, manicures, nail biting, artificial nails, or trauma
Psoriasis plaques, scalp scale, inflammatory back pain, dactylitis, or joint pain
Signs
Longitudinal melanonychia with irregular width/colour or nail dystrophy
Clubbing with loss of nail-bed angle
Fluctuant paronychia or tense pulp-space infection
Multiple nail pitting, oil-drop sign, onycholysis
Subungual debris, thickened brittle yellow nails, associated tinea pedis
Absent cuticle and chronic inflamed nail folds
Approach to Investigation
First-line
Examination of all nails, skin, scalp, and mucosaDetermine single vs multiple nails, pigment pattern, dystrophy, pitting, onycholysis, periungual inflammation, clubbing, and associated dermatoses
Mycological confirmation before systemic antifungalsKOH microscopy, fungal culture, PAS stain of nail clippings, or PCR depending on local access
CBC/ferritin if koilonychia or diffuse brittle nails with systemic symptomsAssesses iron deficiency and anaemia; investigate source when abnormal
CXR or targeted systemic testing for new clubbingGuided by symptoms; evaluate pulmonary, cardiac, GI, hepatic, or malignant causes
Second-line
Nail-matrix biopsyRequired for suspected subungual melanoma or unexplained concerning melanonychia; should be performed by experienced clinician
Blood cultures and echocardiographyIf endocarditis is clinically suspected, not for isolated traumatic splinter haemorrhages
HSV PCRIf herpetic whitlow suspected or vesicular periungual disease is unclear
Specialist
Dermatology referralFor suspected subungual melanoma, complex melanonychia, severe psoriasis, recalcitrant nail disease, or biopsy need
Surgery/podiatry referralFor recurrent ingrown toenail, severe paronychia/felon, diabetic foot involvement, or procedural management
Management Principles
Choosing Wisely Canada dermatology recommendations + MCC Skin and Integument Conditions objective1
Rule out dangerous nail disease
- Urgent dermatology referral for suspicious single-nail melanonychia or Hutchinson sign
- Evaluate new clubbing for systemic disease rather than treating it as a nail problem
- Escalate painful fingertip infection, diabetes, immunosuppression, spreading cellulitis, or suspected felon
2
Treat common nail disorders
- Onychomycosis: confirm mycology first; topical therapy for limited disease; oral terbinafine is common for confirmed significant dermatophyte infection after contraindication/liver-risk review
- Acute paronychia: warm soaks, topical/oral antibiotics when cellulitis exists, and drainage if abscess
- Chronic paronychia: reduce wet work/irritants, protect hands, restore cuticle barrier, topical anti-inflammatory therapy
3
Avoid common harms
- Do not prescribe systemic antifungals without mycological confirmation
- Do not incise herpetic whitlow; use antivirals/supportive care when indicated
- Do not assume every thick dystrophic nail is fungal; psoriasis, trauma, eczema, lichen planus, and tumour are mimics
4
Counselling and follow-up
- Explain nail growth is slow: fingernails take months and toenails may take a year or more to normalize
- Advise footwear/nail trimming strategies for ingrown nails and recurrence prevention
- Safety-net for pigment change, pain, ulceration, spreading infection, or systemic symptoms
Complications & Pitfalls
- Calling melanonychia fungal: A single changing pigmented nail band in an adult needs melanoma assessment.
- Oral terbinafine without confirmation: Choosing Wisely Canada advises mycological confirmation before systemic antifungals.
- Missing clubbing: New clubbing can signal lung cancer, chronic infection, cyanotic heart disease, endocarditis, IBD, or cirrhosis.
- Incising herpetic whitlow: This can worsen outcomes; recognize vesicular painful periungual disease.
- Expecting rapid cure: Nail disorders improve slowly because nail growth is slow.
MCCQE1 Exam Tips
- 1Subungual melanoma clue: single longitudinal pigmented band with Hutchinson sign or change over time
- 2Systemic antifungal therapy for onychomycosis requires mycological confirmation first
- 3Pitting points to psoriasis or alopecia areata; oil-drop sign points strongly to psoriasis
- 4Clubbing is a systemic-disease question, not a dermatology-treatment question
- 5Acute paronychia with abscess needs drainage; chronic paronychia needs irritant avoidance and barrier restoration
- 6Herpetic whitlow has grouped vesicles and pain; do not incise it
- 7Splinter haemorrhages are common after trauma but become important with fever, murmur, or endocarditis risk factors
practicetest your knowledge on nail changesApply what you've learnt with MCCQE1-style questions from the iatroX Q-Bank — dermatologic and beyond.
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