What is the best technique for differentiating between nail psoriasis, nail lichen, and inherited or idiopathic twenty-nail dystrophy syndrome in a patient presenting with nail abnormalities?

Nail Biopsy with Histopathology is the Best Technique for Differentiating These Conditions

The most reliable method to differentiate between nail psoriasis, nail lichen planus, and twenty-nail dystrophy is longitudinal nail biopsy with histopathological examination, as clinical features alone are insufficient for accurate diagnosis. 1

Why Histopathology is Essential

Clinical examination cannot reliably distinguish between these conditions because they share overlapping features such as onycholysis, subungual hyperkeratosis, and trachyonychia. 2, 3 Approximately 50% of dystrophic nails are non-fungal despite similar clinical presentations, highlighting the critical need for definitive diagnostic confirmation. 4

Longitudinal nail biopsy provides diagnostic confirmation in specific cases of acquired nail dystrophy, successfully identifying psoriasis in 4 of 20 cases, lichen planus in 3 cases, and Darier's disease in 1 case in one study series. 1

Specific Histopathological Features to Differentiate

Nail Psoriasis

• Hyperkeratosis with parakeratosis is the most frequent finding (78% of biopsies), followed by neutrophilic infiltration of nail bed epithelium (63%). 2
• Hypergranulosis appears in more than half of nail psoriasis cases (58%), which differs from psoriasis elsewhere on the body. 2
• The nail bed and matrix show these distinctive features that help confirm the diagnosis. 2

Nail Lichen Planus

• Lichen planus produces thinning of the nail plate with subungual hyperkeratosis and longitudinal ridging. 5
• Histopathology reveals features of lichen planus that can be identified on nail biopsy specimens. 1, 6
• Approximately 10% of subjects with lichen planus have abnormal nails, often with thinning of the nail plate, subungual hyperkeratosis, onycholysis, and dorsal pterygium. 7

Twenty-Nail Dystrophy (Trachyonychia)

• Spongiotic changes are found in the majority of cases (19 of 23 patients in one series), with psoriasiform features in 3 patients and lichen planus features in 1 patient. 6
• Spongiotic dermatitis of nail matrix and nail bed with column-like parakeratosis within the nail plate characterizes idiopathic trachyonychia. 8
• The condition is polyetiological, meaning histology helps determine whether it's associated with psoriasis, lichen planus, alopecia areata, or is truly idiopathic. 8

Critical Additional Testing

Always perform PAS (Periodic Acid-Schiff) staining on nail biopsy specimens to exclude fungal infection, as fungal elements were detected in 26% of cases clinically suspected to be psoriasis. 2 The British Association of Dermatologists emphasizes that calcofluor white staining enhances visualization of fungal elements and increases sensitivity compared to potassium hydroxide preparation alone. 7

Clinical Features That Support (But Don't Confirm) Diagnosis

While awaiting histopathology, certain clinical patterns provide clues:

• Nail psoriasis: Distal onycholysis (93.3% of patients) and subungual hyperkeratosis (80%) are most common, with nail pitting and splinter hemorrhages being characteristic. 2
• Nail lichen planus: Post-inflammatory pigmentation on the proximal nail fold, longitudinal fissures, and dorsal pterygium are suggestive features. 3
• Twenty-nail dystrophy: Typical "sandpapered" appearance with rough, lustreless nail plates, or numerous small superficial pits creating a shiny appearance. 6

Common Pitfalls to Avoid

• Never assume diagnosis based on clinical appearance alone—the nail surface in non-infectious conditions typically doesn't become soft and friable as in fungal infection, but visual inspection cannot definitively distinguish between psoriasis, lichen planus, and trachyonychia. 7
• Do not overlook fungal co-infection—even in confirmed inflammatory nail disease, secondary fungal colonization occurs in a significant percentage of cases. 2
• Examine for associated skin findings such as psoriatic plaques, oral lichen planus lesions, or alopecia areata, which can support but not confirm the diagnosis. 7, 6

Practical Biopsy Technique

The longitudinal nail biopsy technique samples both nail matrix and nail bed, providing tissue from the areas where pathological changes originate. 1 This approach yields superior diagnostic information compared to nail clippings or superficial sampling alone.