Nail Disorders and Signs — Clubbing, Koilonychia, Pitting, Terry's and Half-and-Half Nails

Nail signs are classic spotter-style questions: a photograph and the question 'what is the most likely underlying condition?'. The nail unit reflects the health of the matrix, the nail bed and the body: colour changes (leukonychia, half-and-half nails), shape changes (clubbing, koilonychia), surface changes (pitting, Beau's lines) and separation (onycholysis). Each has a short list of causes that you should be able to recite.

The quickest way to revise is by pattern. Use the master table below, then read the detail sections.

Clubbing is soft-tissue swelling of the terminal phalanx with straightening of the angle between the nail bed and the nail. It has been linked to disease since Hippocrates. It can be acquired (infectious, neoplastic, inflammatory or vascular disease), idiopathic, or familial — the familial form is usually dominant. Because isolated clubbing can be benign, the underlying cause still has to be ruled out.

• Pathogenesis (hypothesis): megakaryocytes and platelet clumps bypass the pulmonary capillaries and lodge in the fingertips, releasing PDGF and VEGF, which raise capillary density and permeability; hypoxia enhances their release. The main histological finding is increased capillary density.
• Frequency: clubbing is seen in about 1% of medical admissions, and 40% of those have serious underlying disease. Among thoracic causes, about 80% are due to lung cancer, yet clubbing is present in only 5–15% of lung cancer patients.
• Speed: it can develop in about 2 weeks (new empyema) and reverse in about 2 weeks after corrective cardiac surgery.
• Hypertrophic osteoarthropathy (HOA): subperiosteal new bone at the distal ends of long bones (radius, ulna, tibia, fibula); almost always accompanied by clubbing, especially with bronchogenic carcinoma, other intrathoracic malignancy and cystic fibrosis.
• A chest radiograph is a reasonable first investigation because acquired clubbing is most often pulmonary or cardiovascular.

Koilonychia ('spoon nails') is a nail dystrophy in which the nail plate is thin, brittle and depressed centrally with raised edges. It is frequently seen in chronic iron deficiency from malnutrition, chronic blood loss or malabsorption. It can also be idiopathic, occupational, or associated with rare systemic conditions and alopecia areata. Its presence should prompt a search for iron deficiency.

The mechanism is unclear. It may relate to reduced iron in iron-containing enzymes in the epithelial cells or poor blood flow weakening the nail connective tissue. A peripheral smear in such a patient shows hypochromic microcytes. Revise the anaemias in classification and approach to anaemia and the other nutritional signs in vitamin deficiencies.

Nail psoriasis can be the first presentation of psoriasis, follow it or occur together with it. Nail involvement is a visible predictor of present or future inflammatory joint disease, most prominently of the distal interphalangeal joint, where psoriatic arthritis classically presents. Which change you see depends on which part of the nail unit is involved.

Management depends on extent: mild disease (one or two nails, no functional impairment or systemic disease) is treated topically; disease beyond two nails, or with functional impairment or joint disease, may need systemic therapy, including biologics.

Leukonychia (white nails) is divided into true (abnormal matrix keratinisation — the white colour is in the plate and does not blanch), apparent (the nail bed is abnormal and the white colour fades on pressure) and pseudo-leukonychia (surface fungus). The systemically important signs are the apparent types.

Onychomycosis is a fungal infection of the nail unit. When a dermatophyte causes it, it is tinea unguium. Trichophyton rubrum is the commonest cause; T. mentagrophytes and Epidermophyton floccosum also occur. Dermatophytes account for about 90% of toenail and 50% of fingernail disease, Candida albicans for about 2% (mainly fingernails) and non-dermatophyte moulds for about 8%. Toenails are affected far more often, and an untreated tinea pedis usually precedes the infection. Risk factors include age, diabetes, psoriasis and immunodeficiency. See superficial fungal infections.

• Distal lateral subungual onychomycosis is the commonest type: partial distal onycholysis with subungual hyperkeratosis or crumbling.
• White superficial onychomycosis gives chalky surface deposits that can be scraped off; proximal subungual onychomycosis is the rarest and is associated with AIDS.
• Diagnosis: KOH wet mount is only about 60% sensitive and cannot identify the species; a PAS-stained nail clipping (with Grocott silver) is the most sensitive test, about 95%.
• Treatment: systemic antifungals are most effective. Meta-analysis mycological cure: terbinafine 76%, itraconazole pulse 63%, fluconazole 48%. Check baseline ALT and AST before continuous oral therapy.

Onychomadesis is shedding of the nail: the proximal nail plate separates from the proximal nail fold by a full-thickness sulcus. Causes include trauma, autoimmune disease, major illness, drugs and infection, and among infections hand-foot-mouth disease is the commonest. Growth arrest of the matrix after HFMD gives Beau's lines and onychomadesis weeks after the illness. See picornaviruses: polio and coxsackie.