How do I tell onychomycosis from psoriasis affecting the nail?

Both cause nail plate thickening, discolouration, and onycholysis (separation of nail from bed), making clinical differentiation unreliable in about half of cases. Features favouring onychomycosis: yellow-brown or white discolouration starting at the distal edge or lateral margins, subungual debris, often asymmetrical, toenails more than fingernails, positive nail clipping mycology. Features favouring psoriasis: nail pitting (multiple small ice-pick pits on the nail plate — the most specific sign), oil-drop sign (salmon-coloured subungual patch), salmon nail, red lunula, simultaneous skin psoriasis. eTG and the Australasian College of Dermatologists both advise nail clipping mycology before treating any suspected onychomycosis — false-positive clinical diagnosis is common.

Are oral antifungals for nail fungus safe?

Terbinafine is first-line oral antifungal for dermatophyte onychomycosis and is generally safe. It is a CYP2D6 inhibitor — significant interactions with tricyclic antidepressants, SSRIs, and antipsychotics. Rare but serious adverse effect: drug-induced liver injury; check LFTs at baseline and at 4–6 weeks if symptoms develop or in high-risk patients (pre-existing liver disease, multiple medications). It is not recommended in pregnancy or severe hepatic impairment. Itraconazole is used for non-dermatophyte moulds and candidal onychomycosis; it has more drug interactions (CYP3A4 inhibitor) and cardiac precautions. Both agents require confirmation of fungal infection before prescribing — treat the culture, not the appearance.

What is melanonychia and when does it need a biopsy?

Melanonychia is a brown or black discolouration of the nail plate, typically presenting as a longitudinal streak. It is caused by activation or proliferation of melanocytes in the nail matrix. Causes range from benign (ethnic melanonychia — common and normal in darker skin types, medication-induced, trauma, subungual naevus) to malignant (subungual melanoma). The ABCDEF rule for subungual melanoma: A = age 40–70 + ATSI/African/Asian/Hispanic; B = breadth ≥3 mm, irregular border; C = change in colour or pattern; D = digit (thumb, hallux, or index finger most common); E = extension to proximal nail fold (Hutchinson's sign); F = family or personal melanoma history. Any lesion with Hutchinson's sign (pigmentation extending to periungual skin) needs urgent surgical referral and biopsy. In Fitzpatrick type I–III, any single-nail longitudinal melanonychia warrants dermatology review.

How do I treat an ingrown toenail?

Management depends on severity. Conservative: warm soaks + antiseptic; gutter splinting technique (sliding a sterile tube alongside the offending nail edge). GP procedural: partial nail avulsion under local anaesthetic — removing the ingrown lateral strip with or without phenol ablation of the nail matrix prevents regrowth of that strip. Phenolisation reduces recurrence significantly over simple avulsion. Antibiotics are needed only if there is cellulitis; topical antiseptics are sufficient for localised paronychia. Complete nail avulsion is generally avoided — the whole nail regrows and the problem recurs. Refer to podiatry for initial conservative management, complex cases, and patients with diabetes or peripheral vascular disease (where wound healing is compromised).

What do nail changes tell me about systemic disease?

Nails are a window to systemic disease. Clubbing (Schamroth's sign — loss of the diamond window between opposing nails): lung cancer, bronchiectasis, cyanotic heart disease, IBD, hepatic cirrhosis. Koilonychia (spoon nails): iron deficiency anaemia — also haemochromatosis, hypothyroidism. Leukonychia (white nails): multiple causes including hypoalbuminaemia (Terry's nails — distal brown band), chronic kidney disease (half-and-half nails or Lindsay's nails), zinc deficiency. Beau's lines (transverse grooves across all nails): severe systemic illness, chemotherapy, COVID-19, any significant metabolic stress. Yellow nail syndrome: lymphoedema, chronic respiratory disease, rarely thyroid disease. Single nail signs suggest local pathology; changes in all nails suggest systemic cause.

Nail disease workup

Nail disease workup: the AU general practice approach

By Dr HB Lo, FACRRM Reviewed 26 September 2026 8 min read

Nail disease is a common GP dermatology presentation — fungal infection, psoriatic nail, ingrown toenail, systemic disease markers (clubbing, koilonychia), and pigmented lesions requiring melanoma exclusion.

Key principle: never assume nail discolouration is fungal without mycology. False-positive clinical diagnosis of onychomycosis occurs in up to 50% of cases; nail clipping for microscopy and culture is essential before prescribing oral antifungals.

Red flag: longitudinal melanonychia (single dark streak), especially with Hutchinson's sign (periungual pigmentation). Requires urgent dermatology referral; the ABCDEF criteria guide subungual melanoma detection.

Nails as a clinical examination target

Nail examination is quick, often overlooked, and frequently diagnostic. In Australian general practice, nail complaints account for a significant proportion of dermatology presentations — estimated at 5–10% of all skin-related consultations. The clinical stakes range from a simple structural problem (ingrown toenail) to a diagnosis not to miss (subungual melanoma).

The main categories of nail disease encountered in general practice are: fungal infection (onychomycosis), inflammatory disease (nail psoriasis, lichen planus, eczema), structural nail disorders (ingrown toenail, onychogryphosis, paronychia), pigmentation changes requiring melanoma exclusion, and nail changes as markers of systemic disease.

The single most important diagnostic principle, emphasised by eTG and the Australasian College of Dermatologists: do not prescribe oral antifungals without mycological confirmation. False-positive clinical diagnosis of onychomycosis occurs in up to 50% of cases in published studies. Nail clipping for microscopy and culture is essential.

A. Core clinical — the AU general-practice framework

History to take

RACGP AFP 2017 outlines a systematic approach:

Which nails and how many — single nail vs multiple; fingernails vs toenails vs both; dominant hand first (trauma vs systemic)
Duration and pattern of change — months or years; spreading from one nail to others
Symptoms — pain (ingrown toenail, subacute paronychia, glomus tumour); pruritus (eczema); none (onychomycosis often painless; melanoma asymptomatic until late)
Skin and joint disease — personal or family history of psoriasis (nail psoriasis occurs in 50% of people with plaque psoriasis), eczema, lichen planus
Relevant systemic disease — diabetes (paronychia risk, wound healing); peripheral vascular disease (trophic nail changes, ingrown risks); immunosuppression (candidal onychia); thyroid, renal, or cardiac disease (systemic nail signs)
Medication history — chemotherapy (Beau’s lines, onycholysis); tetracyclines (photo-onycholysis); nail polish, acrylics (irritant contact)
Occupational and hobby exposure — water immersion (candidal paronychia); trauma (haematoma, habit-tic deformity); agricultural/soil exposure (moulds)

Examination

Systematic nail examination requires adequate lighting and ideally magnification (dermatoscope greatly assists):

Nail plate — colour (yellow/brown/white/black/green), texture (pitting, ridging), thickness (thickened in onychomycosis, trauma, psoriasis), surface (granulations = superficial white onychomycosis)
Nail bed — onycholysis (separation from bed); subungual hyperkeratosis (debris); oil-drop sign (psoriasis); splinter haemorrhages; subungual tumour or growth
Nail fold — proximal and lateral: erythema, swelling, tenderness (paronychia); absence of cuticle (chronic paronychia, autoimmune); telangiectasia (nail fold capillaroscopy = connective tissue disease screen)
Matrix — look for surface changes (pits = matrix psoriasis); examine lunula
Periungual skin — Hutchinson’s sign (critical for melanoma)
Schamroth’s sign — for clubbing: press opposing nails together; loss of the diamond window = clubbing

Investigations

Nail clipping for mycology — mandatory before oral antifungals. Collect subungual debris plus clipped nail plate into a dry sterile container. Microscopy (potassium hydroxide preparation) gives rapid result; culture identifies species (dermatophyte vs mould vs candida) and guides treatment choice. Both are needed: culture without microscopy misses dead organisms; microscopy without culture misses species. Sensitivity ~50–80%; false negatives common; treat if clinical picture is convincing with positive microscopy even if culture is negative.
Dermatoscope examination — distinguishes onychomycosis (longitudinal striae, “ruin appearance”, spike pattern) from psoriasis (pitting, oil-drop, irregular salmon patches); greatly reduces misdiagnosis
Nail biopsy — for diagnostic uncertainty in melanonychia, suspected lichen planus, longitudinal erythronychia; refer to dermatology
Bloodwork — if systemic disease suspected: FBC, ferritin, TSH, LFTs, renal function, inflammatory markers

B. Onychomycosis — the most common nail infection

Onychomycosis accounts for ~50% of all nail abnormalities presenting to general practice. Lipner and Scher (JAAD 2019) estimate prevalence at 10% of the general population and up to 20% in adults over 60.

Clinical subtypes

Distal and lateral subungual onychomycosis (DLSO) — the most common; infection enters from the free edge or lateral groove; yellow-brown discolouration and subungual debris spreading proximally
Superficial white onychomycosis (SWO) — white chalky patches on the nail plate surface; usually Trichophyton mentagrophytes; easy to treat topically
Proximal subungual onychomycosis (PSO) — rare; infection enters via the proximal nail fold; suggests immunosuppression (HIV, transplant)
Total dystrophic onychomycosis — end-stage; entire nail involved

Treatment

eTG and AMH recommendations:

Agent	Target	Course	PBS
Terbinafine 250 mg daily	Dermatophytes (first-line)	Fingernails 6 weeks; toenails 12 weeks	Not PBS; OTC or private
Itraconazole pulse (200 mg BD, 1 week/month)	Dermatophytes, moulds, candida	2 pulses fingernails; 3 pulses toenails	Not PBS
Amorolfine 5% nail lacquer	Topical; mild/superficial	6–12 months	OTC
Ciclopirox 8% nail lacquer	Topical; mild disease	48 weeks	Not available in AU

Cure rates: Oral terbinafine achieves mycological cure in ~70–80% for toenail dermatophyte infection (higher for fingernails). Topical agents alone: 15–40% mycological cure for mild disease. Advise patients that nail appearance improves slowly — the nail must grow out, taking 6–12 months for toenails.

Monitoring terbinafine: AMH advises baseline LFTs in patients with pre-existing liver disease or significant alcohol use; routine LFTs not required in healthy patients; check if symptomatic (nausea, jaundice, dark urine).

Recurrence: Common. Address predisposing factors: antifungal powder to footwear and socks, treating tinea pedis (tinea unguium often co-exists with tinea pedis), treating onychomycosis in co-habiting family members.

C. Psoriatic nail disease

Nail involvement occurs in ~50% of people with plaque psoriasis and in ~80% of those with psoriatic arthritis. It significantly impairs quality of life and function. eTG notes it is both underdiagnosed and undertreated.

Distinctive features

Nail pitting — the most specific sign; multiple small, irregular ice-pick pits on the nail plate surface; caused by psoriasis of the nail matrix
Onycholysis — distal separation with discolouration of the free edge; may be mistaken for onychomycosis
Oil-drop sign — salmon-coloured translucent patch visible through the nail plate, caused by psoriasis of the nail bed
Subungual hyperkeratosis — thickening under the free edge
Red lunula — spotted or diffuse erythema of the lunula; specific to psoriasis
Splinter haemorrhages — in psoriasis; also in endocarditis, trauma

Treatment

Mild psoriatic nail disease: potent topical corticosteroid (clobetasol propionate) to the proximal nail fold + nail bed twice daily for 3–6 months; or intralesional triamcinolone injected into the nail fold by a dermatologist. Moderate–severe: escalate to systemic therapy (methotrexate, acitretin) or biologics (TNF inhibitors adalimumab/etanercept, IL-17 inhibitors ixekizumab/secukinumab, IL-23 inhibitors) — refer to dermatology or rheumatology.

D. Australian operations

When to do a nail biopsy

Cancer Council Australia melanoma guidelines and Australasian College of Dermatologists guidance: refer for biopsy when:

Hutchinson’s sign (pigment extending to proximal or lateral nail fold) — urgent
Longitudinal melanonychia ≥3 mm breadth or irregular pattern in Fitzpatrick I–III skin
Any subungual pigmented lesion in a child (paediatric subungual melanoma is rare but exists)
Suspected lichen planus of the nail (dorsal pterygium — progressive dorsal nail fold skin attaching to nail plate) — lateral longitudinal nail biopsy by dermatologist

Ingrown toenail management

The Cochrane review (Eekhof 2012) found phenolisation superior to simple avulsion for preventing recurrence. The GP procedural approach:

Ring-block with 2% lignocaine (digital nerve block, no adrenaline)
Tourniquet applied
Partial nail avulsion — cut and remove the offending lateral strip with Freer elevator; nail splitter if needed
Apply 88% phenol for 3 minutes to the exposed nail matrix → neutralise with 70% isopropyl alcohol
Dress and review at 1–2 weeks
Total avulsion avoided — whole nail regrows, problem returns

Refer to podiatry for: initial conservative management in mild cases; complex cases; diabetes or PVD (specialist assessment of wound healing risk essential).

Systemic disease nail signs — practical table

Sign	Appearance	Systemic associations
Clubbing	Loss of Schamroth’s diamond; soft tissue; increased hyponychial angle	Lung cancer, bronchiectasis, IBD, cirrhosis, cyanotic heart disease
Koilonychia	Spoon-shaped concavity	Iron deficiency, haemochromatosis, hypothyroidism
Terry’s nails	White 80% + distal pink-brown band	Cirrhosis, CCF, CKD, DM
Half-and-half (Lindsay’s)	Proximal white + distal red-brown ≥50%	Chronic kidney disease
Beau’s lines	Transverse grooves all nails	Severe illness, chemo, COVID-19
Onycholysis (all nails)	Separation from bed	Hyperthyroidism, drug (tetracycline, psoralens)
Yellow nail syndrome	Yellow-green, slow growth, absent lunula	Lymphoedema, pleural effusion, rarely thyroid

Biotin note: TGA safety advisory 2019 — biotin supplements (commonly taken for hair and nail growth) interfere with troponin and thyroid function tests. Ask about biotin supplementation before requesting cardiac or thyroid investigations.

E. Special populations

Diabetes mellitus. Diabetic patients are at higher risk for onychomycosis (neuropathy, PVD, hyperglycaemia favouring fungal growth) and also at higher risk of complications from nail procedures. Any nail intervention in a diabetic patient requires careful wound healing assessment; refer to podiatry for routine nail care. Phenolisation is relatively contraindicated in severe ischaemia.

Immunosuppression. Transplant recipients, patients on biologics, and people with HIV are prone to more severe or atypical onychomycosis (including non-dermatophyte moulds, Candida species), proximal subungual pattern, and chronic mucocutaneous candidiasis. Culture with species identification is essential; drug interactions between antifungals and immunosuppressants (tacrolimus × itraconazole = large CNI level rise) are critical.

Pregnancy. Both terbinafine and itraconazole are generally avoided in pregnancy. Topical therapies or deferral of treatment until after delivery are preferred for non-urgent cases. Consult AMH for individual risk assessment.

Children. Onychomycosis is less common in children than adults. Paediatric terbinafine dosing is weight-based; confirm dosing in AMH Children’s Dosing Companion. Melanonychia in children is usually ethnic or traumatic but warrants documentation and dermatology referral for any atypical features.

When to escalate

Urgent dermatology:

Hutchinson’s sign or any suspicious subungual melanonychia
Rapidly progressive nail destruction without obvious cause
Suspected nail lichen planus (risk of permanent nail loss)

General referral:

Nail psoriasis inadequately controlled on topical therapy
Diagnostic uncertainty in onychomycosis despite mycology
Complex ingrown toenail in high-risk patients (diabetes, PVD)
Podiatry for chronic nail care in diabetes

What this article is and is not

This is general health information drawn from current Australian guidelines — eTG, AMH, RACGP, Australasian College of Dermatologists, Cancer Council Australia, and NPS MedicineWise — and major nail disease trials. It is not personal medical advice and does not create a doctor–patient relationship. Decisions about nail biopsy, systemic antifungals, and specialist referral are made with your GP.

For Australian consumer resources: HealthDirect — Nail problems, Australasian College of Dermatologists — A-Z of Skin.

Sources cited

Frequently asked questions

How do I tell onychomycosis from psoriasis affecting the nail?

Both cause nail plate thickening, discolouration, and onycholysis (separation of nail from bed), making clinical differentiation unreliable in about half of cases. Features favouring onychomycosis: yellow-brown or white discolouration starting at the distal edge or lateral margins, subungual debris, often asymmetrical, toenails more than fingernails, positive nail clipping mycology. Features favouring psoriasis: nail pitting (multiple small ice-pick pits on the nail plate — the most specific sign), oil-drop sign (salmon-coloured subungual patch), salmon nail, red lunula, simultaneous skin psoriasis. eTG and the Australasian College of Dermatologists both advise nail clipping mycology before treating any suspected onychomycosis — false-positive clinical diagnosis is common.
Are oral antifungals for nail fungus safe?

Terbinafine is first-line oral antifungal for dermatophyte onychomycosis and is generally safe. It is a CYP2D6 inhibitor — significant interactions with tricyclic antidepressants, SSRIs, and antipsychotics. Rare but serious adverse effect: drug-induced liver injury; check LFTs at baseline and at 4–6 weeks if symptoms develop or in high-risk patients (pre-existing liver disease, multiple medications). It is not recommended in pregnancy or severe hepatic impairment. Itraconazole is used for non-dermatophyte moulds and candidal onychomycosis; it has more drug interactions (CYP3A4 inhibitor) and cardiac precautions. Both agents require confirmation of fungal infection before prescribing — treat the culture, not the appearance.
What is melanonychia and when does it need a biopsy?

Melanonychia is a brown or black discolouration of the nail plate, typically presenting as a longitudinal streak. It is caused by activation or proliferation of melanocytes in the nail matrix. Causes range from benign (ethnic melanonychia — common and normal in darker skin types, medication-induced, trauma, subungual naevus) to malignant (subungual melanoma). The ABCDEF rule for subungual melanoma: A = age 40–70 + ATSI/African/Asian/Hispanic; B = breadth ≥3 mm, irregular border; C = change in colour or pattern; D = digit (thumb, hallux, or index finger most common); E = extension to proximal nail fold (Hutchinson's sign); F = family or personal melanoma history. Any lesion with Hutchinson's sign (pigmentation extending to periungual skin) needs urgent surgical referral and biopsy. In Fitzpatrick type I–III, any single-nail longitudinal melanonychia warrants dermatology review.
How do I treat an ingrown toenail?

Management depends on severity. Conservative: warm soaks + antiseptic; gutter splinting technique (sliding a sterile tube alongside the offending nail edge). GP procedural: partial nail avulsion under local anaesthetic — removing the ingrown lateral strip with or without phenol ablation of the nail matrix prevents regrowth of that strip. Phenolisation reduces recurrence significantly over simple avulsion. Antibiotics are needed only if there is cellulitis; topical antiseptics are sufficient for localised paronychia. Complete nail avulsion is generally avoided — the whole nail regrows and the problem recurs. Refer to podiatry for initial conservative management, complex cases, and patients with diabetes or peripheral vascular disease (where wound healing is compromised).
What do nail changes tell me about systemic disease?

Nails are a window to systemic disease. Clubbing (Schamroth's sign — loss of the diamond window between opposing nails): lung cancer, bronchiectasis, cyanotic heart disease, IBD, hepatic cirrhosis. Koilonychia (spoon nails): iron deficiency anaemia — also haemochromatosis, hypothyroidism. Leukonychia (white nails): multiple causes including hypoalbuminaemia (Terry's nails — distal brown band), chronic kidney disease (half-and-half nails or Lindsay's nails), zinc deficiency. Beau's lines (transverse grooves across all nails): severe systemic illness, chemotherapy, COVID-19, any significant metabolic stress. Yellow nail syndrome: lymphoedema, chronic respiratory disease, rarely thyroid disease. Single nail signs suggest local pathology; changes in all nails suggest systemic cause.

Source quality

Sources grouped by evidence tier. AU primary tier first; international where AU is silent or lagging; named-author reconstruction where guidelines have not yet caught up. How tiers work.