External Medicine
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Nail Diseases
LONGITUDINAL MELANONYCHIA (LM)
Background
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Most common cause: melanocyte activation (melanotic macule). Potentially over 90% of cases. 30765143
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Main goal: rule out melanoma.
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~76% of nail unit melanoma (NUM) come from the nail matrix (SUM). Proximal matrix is most commonly involved as it is the main site of melanocyte activity. 40023404
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Diagnosis
Differentiating Longitudinal Melanonychia from Subungual Melanoma (SUM)
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SUM tends to have wider band width (5.3mm vs 3.1mm for benign LM), take up more percentage of the nail (SUM bands covered ~49.5% of the nail vs 24.8% in benign LM), present for longer duration (129mo vs 39mo), at a younger age (avg 36.1 vs 52 years) have irregular lines sometimes with loss of parallelism. ABCDEF criteria NOT effective at differentiating SUM from benign LM in this study. 30765143
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High risk features and dermoscopy red flags include: monodactylous LM, widening of band, triangular shape/asymmetry, high color intensity or multicolor bands. hutchinson’s sign (pigmentation on periungual skin, NOT through cuticle), nail plate splitting or destruction, width covering ≥40% of the nail plate, rapid change, irregular spacing and thickness of pigmented lines, loss of parallelism, brown background with bands of varying color, thickness, and length. 40023404
Biopsy 40023404
Preferred Technique: Matrix Tangential Excisional Biopsy
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When to use: Lesions ≥3 mm wide, LM suspected to originate in the proximal matrix, no obvious signs of deep invasion.
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Advantages: removes the entire pigmented macule in a thin slice (<1 mm), provides adequate histologic sampling, low risk of permanent onychodystrophy (~26%)
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Limitations: may not capture depth of invasion (i.e., Breslow thickness, less suitable for deep or nodular lesions
For High Suspicion of Invasion: Longitudinal Excisional Biopsy
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When to use: high likelihood of invasive melanoma (iNUM), LM with periungual spread, nail plate destruction, or very wide bands.
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Advantages: samples the entire nail unit: matrix, bed, hyponychium, folds, enables accurate Breslow depth measurement
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Limitations: most invasive, higher risk of nail deformity (splitting, narrowing, misalignment)
MALALIGNMENT OF THE GREAT TOENAIL 39137096
Background
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Definition: a nail that is deviated (usually laterally) from the distal phalanx.
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This weakens the attachment to the nail bed, leads to thickening, yellow-grey-brown discoloration, transverse lines.
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Over time, chronic onycholysis leads to the the lateral nail folds and distal digit pulp "growing in" causing a diminution of the nail bed (disappearing nail bed sign). In basic terms, the chronic separation of the nail bed and plate causes epithelialization of the bed and perpetuates the problem.
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Etiology is unknown, possibly genetic, possibly intrauterine insult. 50% of cases resolve by age 10. Adults presenting with the condition usually endorse prior trauma but this may be delayed presentation of more mild congenital disease.
Treatment
Conservative Management
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Keep nails trimmed short to minimize trauma.
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Use keratolytic agents to soften thickened nails, making them easier to cut.
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Wear well-fitted or open-toed shoes to reduce pressure on the nail.
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Silicone or gel toe caps can protect the nail from trauma.
Cosmetic Solutions
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Acrylic molded nails for improved appearance, though caution is needed to avoid further damage.
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Cosmetic tattooing of the anonychia (absence of nail) after healing from matricectomy (see below)
Medical Interventions
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Steroids:
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High-potency topical steroids or intralesional corticosteroid injections, especially for retronychia (embedded nails).
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Antifungals:
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Treat concurrent fungal infections if present, but this does not resolve malalignment.
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Surgical Interventions
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Realignment Surgery:
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Unguodermal rotation flap for children or select teenagers with mild-to-moderate disease.
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Best performed before age 5, though outcomes may vary in older patients.
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Partial or Total Nail Avulsion:
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Strip avulsion with chemical matricectomy for severe cases with ingrown nails or hypertrophic lateral folds.
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Total nail avulsion with complete matricectomy for "end-stage malalignment.
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RETRONYCHIA (39480960)
Background
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Retronychia is a rare nail disorder characterized by backward growth of the nail plate into the proximal nail fold, causing inflammation, pain, and abnormal nail growth. It typically affects the great toes and is underdiagnosed due to clinical unfamiliarity.
Clinical Features
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All cases involved the great toes.
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Common symptoms: nail thickening (81.3%), yellow discoloration (75.7%), onycholysis (58.9%), discharge, and pain (74.8%).
Causes
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The main cause is chronic mechanical pressure, especially from:
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Wearing socks during sleep (reported by 88.79% of patients)
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Tight or uncomfortable footwear (29.91%)
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History of paronychia (25.23%)
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Intense exercise (19.63%)
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Repetitive nail trauma (14.95%)
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Treatment
Nonsurgical Treatment
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Eliminating triggers like sock-wearing
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79.55% complete recovery
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13.64% partial improvement
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6.82% needed surgery due to recurrence
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Surgical Treatment
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Complete nail avulsion: 90.91% cure rate
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Partial avulsion (sparing inner nail plate): 96.67% cure rate
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Complete avulsion was performed in more severe cases, especially when there was purulent granulation tissue or signs of infection at the proximal nail fold. Partial avulsion, where the innermost nail plate was spared, was reserved for less severe cases, where that inner plate appeared healthy, whitish, and intact. So, the better outcomes with partial avulsion reflect milder initial disease, not necessarily that partial is always more effective.
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Fewer complications (e.g., nail deformity) with partial avulsion