01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Nail signs arise from different anatomy. Matrix disease changes the plate as it is formed, producing pits, ridges, Beau lines or longitudinal pigment. Nail-bed disease causes onycholysis, oil-drop change, subungual material or splinter haemorrhage. Proximal and lateral folds reveal inflammation, infection or pigment spread. Fingernails take roughly six months and toenails twelve to eighteen months to replace, so a groove's distance from the cuticle can place a past event approximately but cannot date it precisely without individual growth rate.
Psoriasis is a common unifying diagnosis, yet fungus frequently coexists and must be confirmed before systemic antifungal treatment. Melanonychia deserves an inclusive approach: benign racial or physiological bands are common in people with deeply pigmented skin and often affect several nails, but this must never become reassurance for a changing irregular single band. Conversely, automatic urgent biopsy of every stable narrow band can cause avoidable permanent dystrophy. Dermoscopy, serial measurement and specialist triage balance those harms.
Systemic associations are clues, not shortcuts. Clubbing can accompany lung cancer, bronchiectasis, interstitial lung disease, cyanotic heart disease and inflammatory bowel or liver disease. Koilonychia prompts iron assessment when history supports it. Terry or half-and-half nails and transverse lines occur with chronic or severe illness but have limited specificity. A good nail examination therefore leads to a focused history, physical examination and selected tests rather than a chart of one-to-one diagnoses.
Key points
- Nails record matrix, bed and systemic events slowly; name the structure and pattern before assigning a disease, because most single signs are not specific.
- Psoriasis causes regular pitting, oil-drop or salmon patches, subungual hyperkeratosis and onycholysis with an erythematous border, and may exist without obvious skin plaques.
- A new evolving irregular longitudinal melanonychia band in one adult nail, especially with periungual Hutchinson pigment or nail destruction, must be assessed urgently for melanoma.
- Longitudinal pigmentation across several nails can be physiological in darker skin or drug related, but change, symptoms and one-nail asymmetry remain important in every skin tone.
- True clubbing includes loss of the nail-fold angle, increased fluctuation and bulbous distal phalanx; it triggers cardiopulmonary, gastrointestinal and inflammatory assessment rather than a cosmetic referral.
- Koilonychia can accompany iron deficiency, while Beau lines mark temporary matrix arrest after severe illness or stress; neither establishes the systemic diagnosis by itself.
- Splinter haemorrhages are commonly traumatic and distal, but multiple proximal lesions plus fever, murmur or embolic features require urgent endocarditis assessment.
- Onycholysis occurs with psoriasis, fungus, trauma, thyroid disease and medicines; clip, examine and sample rather than inferring cause from separation alone.
- Nail-matrix biopsy can permanently alter growth and should be planned by a specialist who can target the lesion and orient histology correctly.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Matrix inflammation
Psoriasis, lichen planus and systemic growth arrest alter plate formation, producing pits, ridges, grooves, thinning or pigment lines.
Nail-bed disease
Psoriasis, fungus, trauma and tumours change adhesion, keratin and vasculature beneath the plate, creating onycholysis, debris or haemorrhage.
Melanocyte activation or proliferation
Physiological pigmentation, medicines, inflammation, naevi and melanoma can each generate longitudinal melanin from the nail matrix.
Systemic tissue signalling
Cardiopulmonary and inflammatory disease can remodel distal digits, while severe illness temporarily arrests matrix growth and iron deficiency alters plate structure.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Matrix defects grow distally
Once plate is formed it cannot repair, so pits, grooves and pigment migrate toward the free edge at the individual's nail-growth rate.
- 2Bed adhesion is disrupted
Inflammation, keratin accumulation or trauma separates plate from bed, allowing air, organisms and debris into the onycholytic space.
- 3Melanin enters the plate
A matrix melanocyte population deposits pigment into growing keratin, producing a longitudinal band whose width and regularity reflect the source.
- 4Distal soft tissue expands
Clubbing involves vascular and connective-tissue change beneath the nail bed, increasing fluctuation and flattening the normal proximal-fold angle.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Regular pits, crumbling and leukonychia arise from matrix inflammation and may accompany scalp, natal-cleft, umbilical or extensor psoriasis.
Oil-drop colour, subungual hyperkeratosis and onycholysis with a salmon-pink proximal margin support nail-bed psoriasis.
A new single band with irregular lines, colour variation, proximal widening, periungual extension or dystrophy raises nail-unit melanoma concern.
Loss of the normal nail-fold angle, increased nail-bed fluctuation, bulbous tips and absent Schamroth window support clubbing when assessed together.
A thin concave spoon-shaped plate can accompany iron deficiency but also occurs after trauma, exposure or as an individual trait.
Transverse depressions at similar levels across several nails record temporary matrix growth arrest after systemic illness, chemotherapy or severe stress.
Thin longitudinal red-brown lines are often distal and traumatic; multiple proximal lesions with fever or embolic features raise endocarditis concern.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
All-nail and skin examinationFirst step - Why
- Define number, symmetry, anatomical structure and associated skin or joint phenotype.
- Interpretation and limitations
- Several similar nails with classic skin psoriasis support a field disorder; a progressive single nail needs focal tumour, trauma or infection assessment.
- 02
Nail dermoscopy - Why
- Assess pigment lines, nail-bed vascular features and an onycholysis margin under magnification.
- Interpretation and limitations
- Irregular line thickness, colour, spacing and periungual spread increase melanoma concern, but dermoscopy cannot replace specialist biopsy when clinical suspicion persists.
- 03
Serial photography and measurement - Why
- Determine whether a low-risk pigmented band is stable or evolving under a specialist plan.
- Interpretation and limitations
- Use calibrated width, proximal and distal landmarks, consistent lighting and a short defined review interval; undocumented observation is not safe surveillance.
- 04
Nail clipping and subungual mycology - Why
- Identify fungal infection where psoriasis, trauma and onychomycosis overlap.
- Interpretation and limitations
- Collect proximal diseased plate and debris before systemic antifungal treatment; positive fungus can coexist with psoriasis and does not explain a suspicious pigment band automatically.
- 05
Nail-unit biopsy - Why
- Establish melanoma, inflammatory matrix disease or another structural diagnosis when the result changes management.
- Interpretation and limitations
- A nail specialist selects matrix, bed or fold target and counsels about pain, scar and permanent dystrophy; superficial clipping cannot exclude a matrix melanoma.
- 06
Cardiopulmonary assessment for clubbing - Why
- Identify a serious thoracic, cardiac or inflammatory cause of true new clubbing.
- Interpretation and limitations
- Use symptoms, oxygen saturation, chest examination and indicated radiography or specialist testing; normal initial observations do not make persistent new clubbing cosmetic.
- 07
Full blood count and ferritin - Why
- Assess iron deficiency when koilonychia or blood-loss history supports it.
- Interpretation and limitations
- Interpret ferritin with inflammation and investigate the cause of deficiency; spooning alone does not justify indefinite iron or prove gastrointestinal bleeding.
- 08
Blood cultures and endocarditis pathway - Why
- Investigate systemic infection when splinter haemorrhages accompany fever, murmur or embolic findings.
- Interpretation and limitations
- Obtain appropriate cultures before antibiotics when this does not delay sepsis treatment, and arrange echocardiography and specialist care from the overall probability.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Onychomycosis
Subungual debris and colour can mimic psoriasis, so representative microscopy and culture are needed before prolonged oral antifungal treatment.
Traumatic dystrophy
Footwear, sport, picking or repetitive work produces local ridges, haemorrhage and onycholysis with a distribution matching mechanical exposure.
Physiological melanonychia
Stable regular bands in several nails are common in darker skin and differ from a new widening irregular single-nail outlier.
Subungual haematoma
Trauma-related blood fails to form orderly longitudinal matrix lines and should migrate distally with plate growth, while persistent atypical pigment needs review.
Periungual squamous malignancy
A persistent verrucous, ulcerated or destructive nail-fold lesion can mimic wart or infection and requires biopsy when treatment fails or invasion is suspected.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Pigmented bandTriage melanonychia without skin-tone biasFirst stepLongitudinal brown or black pigment appears in one or more nails.+
- 1Ask onset, change, trauma, medicines, pregnancy, family pigmentation and melanoma history, then examine every nail, skin and mucosa and photograph with consent.
- 2Refer urgently a new or changing irregular single band, proximal widening, Hutchinson sign, dystrophy, bleeding or mass through the suspected melanoma pathway.
- 3For a genuinely low-risk stable pattern, specialist-led dermoscopic surveillance uses calibrated images and a defined interval; any evolution converts to biopsy assessment.
02Psoriatic nailSeparate inflammation from fungusPitting, oil-drop change, hyperkeratosis or onycholysis suggests psoriasis.+
- 1Look for scalp, ear, umbilical, natal-cleft and extensor disease and ask about inflammatory joint symptoms and functional nail pain.
- 2Obtain representative fungal mycology before oral antifungal treatment when thickening or colour could be infection, recognising that both diagnoses can coexist.
- 3Treat within the psoriasis pathway according to skin, nail and joint burden; isolated severe nail disease can justify dermatology referral even when skin area is small.
03Clubbing or systemic clueInvestigate the person rather than the plateTrue clubbing, koilonychia, Beau lines or widespread new nail change has no obvious local explanation.+
- 1Confirm morphology and timeline, then take respiratory, cardiac, gastrointestinal, bleeding, dietary, medicine and severe-illness history with a directed full examination.
- 2Use oxygen saturation, chest imaging, full blood count, ferritin, liver, renal, thyroid or other tests only as supported by that clinical pattern.
- 3EscalationEscalate hypoxia, haemoptysis, sepsis, murmur or embolic signs immediately and arrange follow-up ownership for less acute unexplained clubbing or systemic change.
04Single destructive nailExclude tumour before repeated treatmentOne nail develops progressive dystrophy, ulceration, bleeding, pain or a subungual mass.+
- 1Document duration and prior trauma or treatment, remove polish and examine plate, bed, folds and regional nodes without curetting a possible tumour.
- 2Arrange urgent dermatology or nail-surgery assessment for dermoscopy, imaging where indicated and properly targeted biopsy.
- 3Do not use repeated antibiotics, antifungals or avulsion as diagnostic substitutes, and ensure histology results and wound care have named clinical ownership.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Delayed melanoma diagnosis
Attributing an evolving pigmented band to ethnicity, trauma or fungus can allow nail-unit melanoma to invade before targeted biopsy.
Missed systemic disease
Failure to investigate true new clubbing or infective endocarditis features delays treatment of potentially life-threatening underlying disease.
Pain and functional loss
Psoriatic, fungal and structural dystrophy can impair grip, walking, footwear tolerance and fine manual tasks despite small body-surface area.
Procedure-induced dystrophy
Poorly planned matrix biopsy, avulsion or destructive treatment can permanently split or deform a nail without obtaining diagnostic tissue.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- For a monitored pigmented band, record calibrated width, colour pattern, proximal widening and periungual pigment at every defined specialist review.
- Track psoriatic nail growth and function over at least six months and reassess mycology before systemic antifungal treatment or unexplained deterioration.
- Follow new clubbing through a named clinician until a plausible cause is identified or an appropriate specialist has accepted ongoing assessment.
- After iron replacement, document haematological response and investigation of blood loss; normal nail shape may take an entire growth cycle to return.
- Following nail-unit biopsy, monitor infection, pain, histology, permanent growth change and whether further excision or oncology discussion is required.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Structure locates disease
Pits originate in matrix, while oil-drop change and onycholysis arise in bed; identifying anatomy narrows both diagnosis and biopsy target.
Several bands can be normal
Physiological melanonychia commonly affects multiple nails in darker skin, but a changing outlier still receives the same melanoma scrutiny.
Clubbing is a composite sign
One curved nail is not enough; angle loss, fluctuation, distal enlargement and distribution together make the finding more reliable.
Nails timestamp imperfectly
A Beau line moves distally as nail grows, offering an approximate record of systemic stress but not a precise calendar date.
Coexistence is common
Psoriatic dystrophy creates spaces in which fungus can grow, so a positive sample does not erase inflammatory signs or joint screening.
11Common pitfallsFrequent interpretation and management errors.
- 01
Reassuring a changing single pigmented band solely because the patient has dark skin.
- 02
Urgently biopsying every stable multi-nail physiological band without specialist dermoscopic triage.
- 03
Diagnosing systemic disease from one nonspecific nail sign without history and examination.
- 04
Calling thick yellow psoriatic nails fungal and prescribing oral terbinafine without sampling.
- 05
Treating splinter haemorrhages cosmetically when fever, murmur or embolic signs are present.
- 06
Performing an unplanned nail-matrix biopsy without consent for permanent dystrophy and histological orientation.