What are the causes of nail dystrophy aside from fungal infections?

Non-Fungal Causes of Nail Dystrophy

Nail dystrophy has numerous non-fungal causes including psoriasis, lichen planus, chronic trauma, bacterial infections, systemic conditions like iron deficiency anemia, and inflammatory disorders that should be considered in differential diagnosis. 1

Common Non-Fungal Causes of Nail Dystrophy

Dermatological Conditions

• Psoriasis: Causes pitting, onycholysis, subungual hyperkeratosis, and oil-drop discoloration of nails 1
• Lichen planus: Presents with thinning of nail plate, subungual hyperkeratosis, onycholysis, and dorsal pterygium 1
• Darier disease: Characterized by longitudinal ridging and V-shaped notches at the free edge of nails 1

Traumatic Causes

• Chronic trauma: Results in distal onycholysis, which can lead to colonization by infectious pathogens and nail discoloration 1
• Repetitive microtrauma: Can be distinguished from fungal infection by examining the nail bed, which appears normal with intact longitudinal epidermal ridges stretching to the lunula 1
• Onychogryphosis: Thickened, curved nails often resulting from chronic pressure or trauma 1

Bacterial Infections

• Pseudomonas aeruginosa: Typically causes green or black discoloration of nails 1
• Bacterial paronychia: Often coexists with fungal infections and may require separate treatment 1

Systemic Conditions

• Iron deficiency anemia: Associated with koilonychia (spoon-shaped nails) and brittle nails 2
• Yellow nail syndrome: Characterized by light green-yellowish pigmentation, hardness, and elevated longitudinal curvature of the nail plate 1
• Peripheral vascular disease: Can cause nail changes similar to proximal subungual onychomycosis 1
• Diabetes mellitus: May present with nail changes resembling fungal infection 3

Other Conditions

• Subungual malignant melanoma: Can mimic fungal nail infection and should be considered in cases of persistent single nail dystrophy 1
• Ichthyotic conditions: Such as keratosis, ichthyosis, and deafness syndrome 1
• Onycholysis: Separation of the nail plate from the nail bed, which can have multiple causes 1

Diagnostic Approach

Key Clinical Features to Distinguish Non-Fungal from Fungal Causes

• Fungal infections typically make the nail surface soft and friable, while non-fungal causes often preserve nail hardness 1
• Distribution patterns can help differentiate causes:
  • Involvement of third or fifth toenails strongly correlates with fungal infection 4
  • Unilateral nail dystrophy, especially affecting multiple nails, suggests fungal etiology 4
  • Dystrophy of all ten nails is less likely to be fungal 4

Essential Diagnostic Tests

• Laboratory confirmation is crucial as approximately 50% of nail dystrophies are non-fungal in origin 2
• Direct microscopic examination using KOH preparation or calcofluor white staining 1
• Fungal culture to identify specific pathogens 1
• Nail clippings for histopathological examination with PAS staining 4
• Consider biopsy for persistent single nail dystrophy to rule out malignancy 1

Management Considerations

Important Pitfalls to Avoid

1. Misdiagnosis: Never assume all nail dystrophies are fungal in origin; laboratory confirmation is essential before initiating antifungal therapy 1, 5
2. Overlooking systemic causes: Nail dystrophy may be a sign of underlying systemic disease requiring investigation 2
3. Inappropriate treatment: Treating presumed fungal infection without confirmation can lead to unnecessary medication exposure and delayed diagnosis of the true cause 1
4. Ignoring bacterial co-infection: Bacterial infections may coexist with fungal infections and require separate treatment 1

Treatment Approach

• Treatment should target the underlying cause rather than just the nail appearance
• For systemic conditions like iron deficiency anemia, addressing the underlying condition will improve nail changes 2
• For dermatological conditions, disease-specific therapy is required (e.g., topical or systemic treatments for psoriasis) 1
• For traumatic causes, removing the source of trauma and allowing the nail to grow out naturally 1

By understanding the diverse non-fungal causes of nail dystrophy and following a systematic diagnostic approach, clinicians can provide appropriate treatment and avoid unnecessary antifungal therapy for patients with nail abnormalities.