What is nail dystrophy?

What is Nail Dystrophy?

Nail dystrophy is an abnormality of the nail unit characterized by altered nail color, shape, texture, or growth pattern, resulting from damage to the nail plate, nail bed, nail matrix, or surrounding tissues. 1

Clinical Definition and Scope

Nail dystrophy encompasses any structural or functional abnormality of the nail apparatus that deviates from normal nail morphology. 2 The term specifically refers to:

• Altered nail plate integrity: Including thickening, thinning, splitting, or complete destruction of the nail plate 1
• Discoloration: Ranging from white to yellow, green, or brown depending on the underlying cause 1
• Textural changes: Such as roughening, ridging (longitudinal or horizontal), pitting, or friability 1, 3
• Growth abnormalities: Including slowed growth, complete growth arrest, or abnormal nail plate formation 4

Anatomical Classification

The clinical presentation depends on which part of the nail unit is affected:

• Nail matrix damage: Produces longitudinal ridging, thinning, and impaired nail plate formation, as seen in inflammatory conditions like lichen planus and psoriasis 5, 4
• Nail bed involvement: Results in onycholysis (separation of nail plate from nail bed), subungual hyperkeratosis, and discoloration 1
• Nail plate surface: Manifests as superficial flaking, white discoloration, or roughening 1
• Nail fold pathology: Leads to proximal nail dystrophy through chronic inflammation and infection of the matrix area 1

Common Etiologies

Infectious Causes

Fungal infections (onychomycosis) account for 50% of all nail dystrophy cases, making them the single most common cause. 1, 6 The British Association of Dermatologists identifies several patterns:

• Distal and lateral subungual onychomycosis (DLSO): The most common presentation, causing nail thickening, discoloration, and onycholysis 1
• Superficial white onychomycosis (SWO): Produces crumbling white lesions on the nail surface 1
• Total dystrophic onychomycosis (TDO): Results in near-complete destruction of the nail plate 1

Bacterial infections, particularly Pseudomonas (Green Nail Syndrome), cause green discoloration and require keeping the area dry with topical povidone iodine 2% twice daily. 5, 6

Inflammatory Conditions

• Psoriasis and lichen planus: Cause nail thinning, longitudinal ridging, and dramatically slowed growth through direct matrix damage 5, 4
• Chronic paronychia: Leads to proximal nail dystrophy, particularly in patients with wet occupations or chronic moisture exposure 1, 4

Drug-Induced Dystrophy

Chemotherapy agents, particularly taxanes, cause dose-related nail changes through direct cytotoxic damage to the nail matrix. 4, 7 Other culprits include:

• EGFR inhibitors, mTOR inhibitors, and MEK inhibitors 4
• Tetracyclines and quinolones (causing photosensitivity-related changes) 7
• Retinoids and psoralens 7

Trauma and Other Causes

• Chronic mechanical trauma: Causes permanent matrix damage preventing normal nail plate formation 4
• Systemic diseases: Various internal conditions can manifest as nail dystrophy 2

Critical Diagnostic Principle

A crucial pitfall: Do not diagnose the cause of nail dystrophy based on clinical appearance alone, as 50% of dystrophic nails are non-fungal despite similar presentation. 5, 6, 4 The British Association of Dermatologists mandates laboratory confirmation before initiating treatment:

• Direct microscopy with potassium hydroxide (KOH) preparation to visualize fungal elements 5, 6, 4
• Fungal culture on Sabouraud's glucose agar to identify the specific organism 5, 6
• Calcofluor white staining significantly enhances visualization of fungal elements 6, 4
• Bacterial culture if green discoloration suggests Pseudomonas infection 4

Functional and Psychosocial Impact

Nail dystrophy causes:

• Impaired hand or foot function due to the important mechanical role of nails 8
• Pain or discomfort, particularly with ingrown nails, inflammation, or abscesses 7
• Significant psychosocial effects: Including reduced employability, diminished self-esteem, and impaired social interaction 8
• Cosmetic concerns that may require nail cosmetics as supportive therapy while awaiting treatment efficacy or when damage is irreversible 8

Treatment Timeline Considerations

Toenails require approximately 12 months to grow out completely, while fingernails take about 6 months, making this far too long to await results of a therapeutic trial without confirmed diagnosis. 1 Most drug-induced nail dystrophies resolve after discontinuation, though complete resolution sometimes takes several years. 7