Possible causes of multiple onychodystrophy include fungal nail infection (onychomycosis), psoriasis, lichen planus, eczema, alopecia areata, bacterial infections, trauma, yellow nail syndrome, periungual squamous cell carcinoma, and subungual malignant melanoma. Fungal nail infection is the commonest cause and can affect multiple nails, particularly toenails, and is caused by dermatophytes, yeasts (such as Candida species), and non-dermatophyte moulds NICE CKS. Psoriasis may present with nail pitting, subungual hyperkeratosis, and dystrophy NICE CKS. Lichen planus nails may be thin or thickened, grooved, and discoloured, sometimes with nail shedding NICE CKS. Eczema and alopecia areata may also cause ridged, brittle, or pitted nails NICE CKS. Bacterial infections (notably with Pseudomonas aeruginosa) may cause colour changes, while trauma can lead to nail abnormalities resembling fungal infection NICE CKS. Yellow nail syndrome manifests as green-yellow discoloration, hard nails with curvature, and nail shedding and is associated with respiratory and lymphatic conditions NICE CKS. Malignant causes typically affect single nails but should be considered NICE CKS.
Management options depend on the underlying cause but for fungal nail infection include self-care measures such as keeping nails short, wearing non-occlusive footwear, and treating any coexisting fungal skin infections. Mild, limited fungal infections of up to two nails may be treated with topical antifungal lacquers such as amorolfine 5% NICE CKS,SmPC Curanail,SmPC Care,SmPC Amorolfine. If topical treatment is inappropriate or unsuccessful, oral antifungals like terbinafine (first-line for dermatophytes) or itraconazole/fluconazole (for Candida or non-dermatophytes, off-label) may be indicated NICE CKS. Nail regrowth should be assessed after 3–6 months of treatment NICE CKS. In cases of treatment failure, managing underlying causes, re-sampling for fungal culture, combined topical and oral treatment, or referral to specialists may be necessary NICE CKS.
For other causes like psoriasis, specialist treatments include topical calcineurin inhibitors, phototherapy, systemic or biologic therapies depending on severity and impact. The choice of management should consider the functional or cosmetic impact and psychological wellbeing NICE CKS.