Residency · Residency · Dermatology
Nail Disorders: Diagnosis and Management
Introduction
The nail unit is a complex structure that reflects both local disease processes and systemic conditions. A systematic approach to nail examination, combined with understanding of nail anatomy and growth kinetics, enables accurate diagnosis and targeted therapy. This lecture covers the most clinically significant nail disorders encountered in dermatology practice.
Nail Anatomy and Physiology
The nail matrix is the germinative epithelium that produces the nail plate, with the proximal matrix producing the dorsal nail plate and the distal matrix producing the ventral nail plate. The lunula is the visible, pale crescent representing the distal matrix. The nail plate is composed of hard keratins (K31, K85, K86) and grows at approximately 3 mm per month for fingernails and 1 mm per month for toenails. The nail bed is the epithelium beneath the nail plate and produces a thin layer that contributes to plate thickness. The hyponychium is the seal between the distal nail bed and the nail plate. The proximal nail fold (PNF) covers the proximal matrix and produces the cuticle (eponychium). The lateral nail folds contain the lateral nail plate margins.
Approach to Nail Diagnosis
A systematic evaluation begins with the history, addressing onset, duration, number of nails affected, medications, occupational exposures, trauma, and associated skin or joint disease. Examination should include all 20 nails, assessing color, surface, thickness, shape, and periungual tissue. Dermoscopy (onychoscopy) evaluates subungual pigmentation, vascular patterns, and surface changes. A nail clipping for PAS stain and culture is first-line for suspected onychomycosis. Nail biopsy options include matrix biopsy (for surface abnormalities), nail bed biopsy (for subungual lesions), or longitudinal excisional biopsy (for melanonychia).
Common Nail Disorders
Onychomycosis
Onychomycosis is the most common nail disorder, affecting 10% of the general population with prevalence increasing with age. Causative organisms include dermatophytes (90%, with Trichophyton rubrum being most common), non-dermatophyte molds (Fusarium, Aspergillus), and yeasts (Candida).
The clinical subtypes are as follows. Distal lateral subungual onychomycosis (DLSO) is the most common, spreading from the hyponychium proximally and presenting with subungual hyperkeratosis, onycholysis, and yellow-white discoloration. Proximal subungual onychomycosis (PSO) spreads from beneath the PNF and is associated with immunosuppression, serving as an HIV indicator. White superficial onychomycosis (WSO) produces white, chalky patches on the dorsal nail plate surface. Total dystrophic onychomycosis is the end-stage of any subtype with complete nail destruction.
Diagnosis should always be confirmed before treating. A nail clipping for PAS stain (sensitivity 82%) is superior to KOH (sensitivity 60%). Fungal culture provides speciation, and PCR-based assays are also available. Treatment for mild DLSO without matrix involvement (less than 50% nail affected) uses topical agents such as efinaconazole 10% or tavaborole 5% solution. Systemic therapy with terbinafine (250 mg daily for 6 weeks for fingernails, 12 weeks for toenails) is first-line, with baseline LFTs recommended. Itraconazole pulse dosing (200 mg twice daily for 1 week per month for 3 to 4 months) is an alternative for terbinafine-intolerant patients or non-dermatophyte molds. Combination topical plus systemic therapy improves cure rates. Cure rates remain modest (complete cure approximately 50 to 70%), and recurrence is common.
Nail Psoriasis
Nail psoriasis affects 40 to 50% of psoriasis patients and up to 80% of psoriatic arthritis patients. Nail matrix disease produces pitting (the most common finding, with small, regular depressions), leukonychia, red spots in the lunula, and nail plate crumbling. Nail bed disease produces the oil-drop (salmon patch) discoloration, onycholysis, subungual hyperkeratosis, and splinter hemorrhages. The key distinction from onychomycosis is that psoriatic pitting is regular and geometric, the oil-drop sign is characteristic of psoriasis, fungal cultures are negative, and the clinical context of skin and joint disease provides diagnostic support. Treatment includes topical corticosteroids (high potency under occlusion), intralesional triamcinolone (2.5 to 5 mg/mL injected into the proximal nail fold), calcipotriol, and topical tazarotene. Systemic agents are used for refractory cases, with biologics being highly effective for nail psoriasis.
<image>Clinical photograph comparison of nail psoriasis features (regular pitting, oil-drop discoloration, onycholysis) versus onychomycosis features (subungual hyperkeratosis, yellow-brown discoloration, DLSO pattern) with labeled annotations</image>
Lichen Planus of the Nail
Nail lichen planus affects 10% of patients with cutaneous LP and may occur in isolation. Matrix involvement produces thinning of the nail plate, longitudinal ridging, fissuring, and dorsal pterygium, a scarring attachment of the PNF to the nail bed with V-shaped loss of the nail plate. Twenty-nail dystrophy (trachyonychia) describes a rough, sandpaper-like surface of all 20 nails and may be caused by LP, alopecia areata, psoriasis, or eczema. Dorsal pterygium is the hallmark and is pathognomonic for nail LP, representing irreversible matrix scarring. Treatment urgency is emphasized because aggressive early treatment can prevent permanent nail loss. Options include intralesional triamcinolone to the matrix, systemic corticosteroids for rapidly progressive disease, and hydroxychloroquine.
Melanonychia
Longitudinal melanonychia (LM) presents as a brown-black longitudinal band within the nail plate. The differential diagnosis includes melanocytic activation (the most common cause, from friction, trauma, medications, or inflammatory conditions), lentigo, nevus, and subungual melanoma. Subungual melanoma must always be considered, as it accounts for 1.5 to 3.5% of all melanomas and represents a higher proportion in Black, Hispanic, and Asian populations.
The ABCDEF criteria help identify concerning melanonychia: Age 40 to 70 years, Band that is brown-black with breadth greater than 3 mm and irregular borders, Change with rapid evolution in size, color, or morphology, Digit (thumb, great toe, or index finger as the most common sites), Extension with the Hutchinson sign (pigment extending to the proximal or lateral nail folds), and Family or personal history of melanoma.
Dermoscopy of melanonychia can help distinguish benign from malignant causes: regular, parallel lines suggest a benign process, while irregular lines, loss of parallelism, and a micro-Hutchinson sign (pigment visible only on dermoscopy) suggest melanoma. A longitudinal excisional biopsy of the matrix is the gold standard for histologic evaluation.
Ingrown Nails (Onychocryptosis)
Ingrown nails occur when the lateral nail plate penetrates the lateral nail fold, most commonly affecting the great toe. Risk factors include improper nail trimming (cutting too short or curved), tight footwear, nail dystrophy, obesity, and hyperhidrosis. Staging includes Stage I (erythema, edema, mild tenderness), Stage II (granulation tissue, infection, increased pain), and Stage III (chronic granulation tissue, hypertrophy of the lateral nail fold). Treatment for Stage I is conservative with proper trimming, cotton wick elevation, and soaking. Stages II and III require partial nail avulsion with phenol matricectomy (chemical destruction of the lateral matrix) for definitive cure, with a success rate exceeding 95%.
<image>Dermoscopic images of longitudinal melanonychia comparing a benign melanocytic nevus showing regular, parallel brown lines with a subungual melanoma showing irregular line spacing, variable line thickness and color, and micro-Hutchinson sign with pigment extending to the proximal nail fold</image>
Nail Signs of Systemic Disease
Clubbing (increased nail plate curvature and soft tissue hypertrophy of the distal digit) is associated with pulmonary disease, cardiac disease, IBD, and hepatic cirrhosis. Koilonychia (spoon nails) with concave, spoon-shaped nails is associated with iron deficiency anemia. Beau's lines are transverse depressions representing temporary growth arrest from a systemic insult (severe illness, high fever, chemotherapy), and the insult can be dated based on nail growth rate. Mees lines are transverse white bands associated with arsenic poisoning, thallium, chemotherapy, and severe systemic illness. Muehrcke lines are paired, transverse white bands that disappear with pressure, associated with hypoalbuminemia. Terry nails show proximal two-thirds white with a normal distal band and are associated with hepatic cirrhosis, congestive heart failure, and diabetes. Half-and-half nails (Lindsay nails) show proximal white and distal brown coloration, associated with chronic kidney disease. Yellow nail syndrome features slow-growing, thickened, yellow nails with lymphedema and pleural effusions.
| Nail Sign | Appearance | Associated Conditions |
|---|---|---|
| Clubbing | Increased curvature, bulbous digit | Pulmonary disease, cardiac disease, IBD, cirrhosis |
| Koilonychia | Concave (spoon-shaped) | Iron deficiency anemia |
| Beau's lines | Transverse depressions | Severe systemic illness, high fever, chemotherapy |
| Mees lines | Transverse white bands | Arsenic, thallium, chemotherapy |
| Muehrcke lines | Paired white bands (disappear with pressure) | Hypoalbuminemia |
| Terry nails | Proximal 2/3 white, distal normal | Cirrhosis, CHF, diabetes |
| Half-and-half (Lindsay) | Proximal white, distal brown | Chronic kidney disease |
| Yellow nail syndrome | Thick, yellow, slow-growing | Lymphedema, pleural effusions |
Nail Tumors
Myxoid (digital mucous) cysts are dome-shaped, translucent nodules over the DIP joint or PNF, connected to the joint space, that produce a longitudinal groove in the nail plate from matrix compression. Treatment includes drainage, intralesional corticosteroids, or surgical excision. Glomus tumors are benign vascular tumors of the glomus body presenting with the classic triad of pinpoint tenderness, cold sensitivity, and paroxysmal pain, with blue-red discoloration visible through the nail plate. MRI confirms the diagnosis, and surgical excision is curative. Subungual exostosis is a bony outgrowth from the distal phalanx presenting as a firm, painful nodule elevating the nail plate, confirmed by X-ray and treated with surgical excision. Periungual fibromas (Koenen tumors) are flesh-colored, elongated nodules arising from beneath the PNF and are pathognomonic for tuberous sclerosis complex.
Key Clinical Pearls
Onychomycosis should always be confirmed with laboratory testing before initiating systemic antifungals, as clinical mimics are numerous. Proximal subungual onychomycosis in an otherwise healthy young patient warrants HIV testing. Any solitary longitudinal melanonychia in an adult that is new, changing, or meets ABCDEF criteria requires matrix biopsy to exclude melanoma. Dorsal pterygium is pathognomonic for nail lichen planus and represents irreversible damage, making early aggressive treatment essential to prevent this outcome. Nail psoriasis is often undertreated but significantly impacts function and quality of life; biologic therapies provide the most consistent nail clearance.
<image>Composite clinical image showing nail signs of systemic disease: clubbing with increased Lovibond angle, koilonychia with concave nail plate, Beau lines with transverse grooves, and half-and-half nails with proximal white and distal brown coloration</image>
References
- Lipner SR, Scher RK. Onychomycosis: clinical overview and diagnosis. J Am Acad Dermatol. 2019;80(4):835-851.
- Rich P, Scher RK. Nail psoriasis severity index: a useful tool for evaluation of nail psoriasis. J Am Acad Dermatol. 2003;49(2):206-212.
- Levit EK, Kagen MH, Scher RK, Grossman M, Altman E. The ABC rule for clinical detection of subungual melanoma. J Am Acad Dermatol. 2000;42(2 Pt 1):269-274.
- de Berker DA. Nail anatomy. Clin Dermatol. 2013;31(5):509-515.
