Nail Psoriasis
Nail psoriasis is a chronic immune-mediated inflammatory condition that affects about 50% of people with skin psoriasis and as many as 80–90% of those with psoriatic arthritis (PsA). Nail involvement is an independent predictor of progression to psoriatic arthritis and can severely reduce quality of life (DLQI).
The underlying driver is abnormal activation of the IL-23/Th17/IL-17A axis together with TNF-alpha, which causes excessive proliferation of keratinocytes and dilation of the looped capillaries in the nail unit. Clinical signs fall into two main anatomical groups:
- Nail matrix involvement:
- Incomplete keratinization (parakeratosis) leaves clusters of abnormal keratin cells within the growing nail plate. As the nail grows out, these clusters flake away, leaving small saucer-shaped depressions known as nail pitting.
- Nail bed involvement:
- Neutrophil infiltration (Munro microabscesses) and inflammatory exudate in the nail bed epithelium alter its appearance, producing the characteristic yellow-orange to salmon-pink discoloration known as the oil-drop sign or salmon patch.
- Overgrowth of keratin in the nail bed pushes the nail plate up from its attachment (onycholysis), leaving a space where bacteria and fungi can move in.
Nails affected by psoriasis carry a risk of secondary fungal infection (onychomycosis) of up to 25–30%, because the nail separates and keratin builds up beneath it. At Haute-Derma, every diagnosis combines nail dermoscopy (onychoscopy) to look for scattered capillary loops with KOH microscopy, PAS staining or fungal culture before treatment begins. This avoids using corticosteroids alone, which can make a fungal infection flare, or treating with antifungals alone and missing the underlying psoriasis.
Clinical Features and the NAPSI Severity Score
- Nail matrix signs:
- Pitting: Depressions 0.5–2 mm across, randomly distributed, with a rough base.
- Red spots in the lunula: Red dots appear in the lunula from congested, dilated capillaries.
- Nail plate crumbling (severe matrix dystrophy): When inflammation of the matrix is severe, the entire nail plate crumbles and becomes completely deformed.
- Nail bed signs:
- Oil-drop sign (salmon patch): A pathognomonic sign: a translucent pink-orange-yellow discoloration beneath the nail plate.
- Onycholysis with an erythematous border: The nail plate separates from the nail bed, and there is always a red-orange rim where attached and detached nail meet, unlike onycholysis caused by trauma.
- Subungual hyperkeratosis: Dense whitish-yellow keratin builds up under the nail plate.
- Splinter hemorrhages: Fine brown-black lengthwise streaks from ruptured nail bed capillaries.
The NAPSI Score (Nail Psoriasis Severity Index)
NAPSI is the standardized tool for grading the severity of nail psoriasis:
- Each nail is divided into 4 quadrants.
- Eight features are assessed (4 matrix features plus 4 nail bed features):
- Matrix: pitting, leukonychia, red spots in the lunula, nail plate crumbling.
- Nail bed: oil-drop sign, onycholysis, subungual hyperkeratosis, splinter hemorrhages.
- Each quadrant showing a sign scores 1 point, giving each nail a score of 0–8.
- Total NAPSI: up to 80 points for the 10 fingernails, or 160 points for all 20 fingernails and toenails.
- NAPSI < 10: mild.
- NAPSI 10–30: moderate.
- NAPSI > 30: severe to very severe (an indication for systemic or biologic treatment).
Nail Psoriasis vs. Onychomycosis vs. Nail Lichen Planus
| Nail Psoriasis | Onychomycosis | Nail Lichen Planus |
|---|---|---|
| Chronic auto-inflammatory disease | Dermatophyte or yeast infection (Trichophyton, Candida) | Autoimmune destruction of keratinocytes |
| Pitting very common, randomly scattered | Pitting rare | No pitting |
| Oil-drop sign present (pathognomonic) | No oil-drop sign | No oil-drop sign |
| Red-orange rim around the detached area | Opaque yellow-white, jagged edge | Nail plate thins progressively from the base |
| Psoriatic skin lesions, finger joint pain | Often with athlete's foot (tinea pedis) | Oral mucosal lesions, lichenoid skin papules |
| Dilated looped capillaries (dotted vessels) | Jagged edge with spikes pointing toward the nail base (spike pattern) | Deep longitudinal ridges, pterygium |
| KOH/PAS negative | Spores or hyphae seen | KOH/PAS negative |
Treatment and Medical Procedures at Haute-Derma
Nail psoriasis calls for a stepwise approach guided by the NAPSI score and by whether the matrix or the nail bed is mainly affected.
Topical Therapy (Mild Disease, NAPSI < 10)
- Clobetasol propionate 0.05% + calcipotriol 0.005% (foam, ointment or gel):
- Apply to the proximal nail fold for matrix disease, or drop under the lifted nail for nail bed disease, once or twice daily for 8–12 weeks.
- Tazarotene 0.1% (topical retinoid):
- Effectively reduces subungual hyperkeratosis and onycholysis.
- Protective medical nail lacquer (hydroxypropyl chitosan, polyureaurethane): Forms a barrier against mechanical and chemical injury.
Intralesional Injection (ILI)
The first-line and most effective option when psoriasis is limited to a few nails (1–4 severely affected nails) or does not respond to topical treatment.
- Drug: triamcinolone acetonide (TAC) 2.5–5.0 mg/mL.
- Injection technique:
- Inject into the proximal nail fold to treat matrix changes (pitting, crumbling).
- Inject into the lateral nail fold to treat nail bed changes (onycholysis, hyperkeratosis).
- Dose: 0.1 mL per injection site, 2–4 sites per digit.
- Frequency: every 4–6 weeks, for a course of 3–5 sessions.
- Note: Pain is controlled with a digital nerve block or by applying cold before the injection.
Systemic and Biologic Therapy
Indicated when NAPSI is above 30, when many nails are involved along with moderate to severe skin psoriasis, or when psoriatic arthritis (PsA) is present.
