Fingernail Dents (Koilonychia/Beau's Lines): Causes, Diagnosis & Clinical Significance
Nail dents—whether spoon-shaped (koilonychia) or transverse grooves (Beau's lines)—signal underlying systemic or local pathology requiring evaluation.
Types of Nail Dents
- Koilonychia (spoon nails): Central concavity, thin edges — holds water drop
- Beau's lines: Transverse grooves across nail plate — growth arrest lines
- Pitting: Pinpoint depressions — psoriasis, alopecia areata
- Longitudinal ridges: Aging, trauma, lichen planus
Systemic Causes
| Cause | Typical Nail Finding | Mechanism |
|---|---|---|
| Iron deficiency anemia | Koilonychia | Impaired nail matrix keratinization |
| Vitamin B12 deficiency | Hyperpigmentation, brittleness | Megaloblastic matrix changes |
| Folate deficiency | Similar to B12 | Impaired DNA synthesis |
| Zinc deficiency | Beau's lines, paronychia | Matrix enzyme dysfunction |
| Protein malnutrition | Beau's lines, Muehrcke lines | Hypoalbuminemia |
| Thyroid disease (hypo/hyper) | Brittle, slow growth, onycholysis | Metabolic dysregulation |
| Diabetes | Beau's lines, yellowing, onychomycosis risk | Vascular, neuropathic, immune |
| Renal/liver disease | Half-and-half nails, Terry's nails | Uremia, hypoalbuminemia |
| Inflammatory bowel disease | Beau's lines (flares) | Malabsorption, inflammation |
| Autoimmune (lupus, RA, scleroderma) | Periungual changes, pitting | Vascular, inflammatory |