What are the possible causes of nail pitting (finger‑nail depressions) and what initial work‑up and management should be undertaken?

Nail Pitting (Fingernail Depressions): Causes and Management

Nail pitting is most commonly caused by psoriasis, affecting approximately 50% of all psoriatic patients and up to 90% of those with psoriatic arthritis, making it the primary diagnosis to consider when evaluating fingernail depressions. 1

Primary Differential Diagnosis

Psoriasis (Most Common Cause)

• Psoriasis is the leading cause of nail pitting, with fingernails involved in approximately 50% of all psoriatic patients and toenails in 35%. 1
• Look for additional nail changes that strongly suggest psoriasis: onycholysis (nail separation), subungual hyperkeratosis (debris under nail), oil-drop sign (yellow-brown discoloration), and nail plate dystrophy. 1, 2
• Up to 90% of patients with psoriatic arthritis demonstrate nail changes, making nail examination crucial for identifying joint involvement. 1
• Examine the skin for characteristic salmon-pink plaques with silvery scale on extensor surfaces, scalp, or in body folds to support the diagnosis. 1

Alopecia Areata

• Alopecia areata commonly presents with nail pitting affecting multiple nails, often accompanied by hair loss patches on the scalp or body. 3
• This diagnosis should be considered when nail pitting occurs in the absence of skin plaques or joint symptoms. 3

Fungal Infection (Less Common for Isolated Pitting)

• Fungal infections typically cause nail thickening, discoloration, and friable texture rather than isolated pitting. 4, 2
• Transverse grooves or pitting with painful perionyx inflammation suggests Candida infection, particularly with repeated water exposure. 2
• The British Journal of Dermatology warns that 50% of dystrophic nails are non-fungal despite similar appearance, making laboratory confirmation essential before diagnosing fungal infection. 4, 2

Lichen Planus

• Lichen planus produces nail-plate thinning with longitudinal ridging and occasional pigmentation, though pitting is less characteristic. 4, 5

Initial Diagnostic Work-Up

Clinical Examination

• Examine all 20 nails systematically to determine whether changes are localized (suggesting trauma or tumor) or generalized (suggesting systemic disease). 6
• Assess for psoriatic features: onycholysis, oil spots, subungual hyperkeratosis, and nail plate dystrophy. 1, 2
• Evaluate nail texture: soft and friable suggests fungal infection, while hard and brittle indicates non-infectious causes. 5
• Check for paronychia (nail fold swelling/erythema), which suggests Candida infection with occupational moisture exposure. 5

Skin and Joint Assessment

• Perform a complete skin examination looking for psoriatic plaques, particularly on elbows, knees, scalp, and gluteal cleft. 1
• Assess for joint pain, swelling, or morning stiffness that might indicate psoriatic arthritis. 1
• Look for patches of hair loss that would support alopecia areata. 3

Laboratory Confirmation (When Fungal Infection Suspected)

• Do not diagnose fungal infection based on appearance alone—the American Academy of Dermatology recommends collecting samples from discolored or dystrophic areas for direct KOH examination and fungal culture. 2
• Collect subungual debris from the most proximal part of the infection using a dental scraper, submitting as much material as possible. 5
• Use calcofluor white staining to enhance visualization of fungal elements compared to KOH alone. 4, 2
• Mycological confirmation is mandatory before initiating antifungal therapy, as 50% of dystrophic nails are non-fungal. 5

When to Consider Biopsy

• The American Academy of Dermatology recommends nail biopsy in cases of uncertain diagnosis after clinical evaluation and negative mycological tests, particularly if suspecting lichen planus, systemic lupus erythematosus, or other rare causes. 2

Management Algorithm

For Psoriatic Nail Disease (Most Common)

• For involvement of less than 3 nails, the American Academy of Dermatology recommends intralesional triamcinolone acetonide 5-10 mg/cc for nail matrix involvement. 5
• Apply topical steroids with or without vitamin D analogs for nail bed involvement. 5
• Psoriasis of the nails is a significant therapeutic challenge, often requiring referral to dermatology for more extensive involvement. 1

For Confirmed Fungal Infection

• Terbinafine is the preferred first-line treatment for dermatophyte onychomycosis: weight-based dosing of 62.5 mg daily (<20 kg), 125 mg daily (20-40 kg), or 250 mg daily (>40 kg) for 6 weeks (fingernails) or 12 weeks (toenails). 4
• Itraconazole pulse therapy (5 mg/kg/day for 1 week per month) for 2 pulses (fingernails) or 3 pulses (toenails) is equally effective, particularly when Candida species are suspected. 4
• Baseline liver function tests and complete blood count are recommended for patients on terbinafine. 4

For Candida-Related Paronychia

• Keep the affected area dry and apply topical povidone iodine 2% twice daily. 4, 5
• Avoid prolonged water exposure and use protective gloves during wet work. 5
• Azoles are preferred when onychomycosis is caused by Candida species. 4

Supportive Care for All Causes

• Apply daily topical emollients to cuticles and periungual tissues to maintain hydration. 5
• Use protective nail lacquers to limit water loss from the nail plate. 5
• Avoid trauma, nail biting, use of nails as tools, prolonged water soaking, and exposure to harsh chemicals. 5

Critical Pitfalls to Avoid

• The most common cause of treatment failure is incorrect diagnosis based solely on clinical grounds without laboratory confirmation. 5
• Do not assume fungal infection without mycological testing—multiple non-infectious causes produce similar appearance. 2, 5
• Inadequate specimen collection from superficial nail plate rather than proximal subungual debris contributes to false negatives. 5
• Never overlook examination of family members for fungal infections, as household transmission is common. 4
• Do not miss melanoma—any dark longitudinal band warrants urgent evaluation to exclude malignancy. 6, 7