What is Onychodystrophy?
Onychodystrophy is the temporary or permanent abnormal change in nail structure, encompassing a broad spectrum of pathologic processes affecting the nail plate, nail bed, or nail matrix. 1, 2
Definition and Scope
Onychodystrophy represents various pathologic processes of the nails including both infectious and noninfectious disorders. 2 The term describes any structural abnormality of the nail apparatus, ranging from mild surface changes to complete nail destruction. 1
Major Categories of Onychodystrophy
Infectious Causes
Onychomycosis is the most common infectious cause, accounting for approximately 50% of all onychodystrophy cases. 3 This includes:
- Distal and lateral subungual onychomycosis (DLSO), the most common presentation with thickened, discolored nails and nail bed separation. 4, 5
- Superficial white onychomycosis (SWO), presenting as crumbling white lesions on the nail surface. 4, 5
- Proximal subungual onychomycosis (PSO), starting from the proximal nail and common in immunocompromised patients. 4, 5
- Total dystrophic onychomycosis (TDO), where the nail plate is almost completely destroyed. 4
Candidal infections cause 5-10% of cases, more commonly affecting fingernails through chronic paronychia with secondary nail dystrophy. 4, 5
Bacterial infections, particularly Pseudomonas aeruginosa, cause green or black nail discoloration. 4, 5
Inflammatory and Dermatologic Causes
Psoriasis produces nail changes including thinning, subungual hyperkeratosis, onycholysis, and ridging. 4, 6, 5
Lichen planus affects approximately 10% of patients with the condition, causing nail thinning, longitudinal ridging, subungual hyperkeratosis, and dorsal pterygium. 4, 6, 5
Darier disease is a rare genetic disorder causing nail dystrophy including ridging. 4, 6
Traumatic Causes
Repetitive trauma results in distal onycholysis leading to colonization by infectious pathogens and nail plate discoloration. 4, 6, 5
Chronic moisture exposure in wet occupations causes chronic paronychia with secondary nail dystrophy. 4, 5
Idiopathic Onychodystrophy
- Many cases have no identifiable underlying cause and are classified as idiopathic. 1 These cases are particularly challenging to treat, with limited therapeutic options available. 1
Clinical Significance
The key diagnostic challenge is that most nail changes are nonspecific, making it difficult to establish the diagnosis based on appearance alone. 2 Nail changes may be a clue to other dermatological or systemic diseases. 2
Critical Diagnostic Pitfall
Never diagnose fungal infection based on appearance alone—laboratory confirmation with microscopy and culture is mandatory, as 50% of dystrophic nails are non-fungal. 5, 3 To distinguish between nail trauma and infection, examine the nail bed after clipping: normal longitudinal epidermal ridges stretching to the lunula indicate trauma rather than infection. 4, 5
Specific Nail Dystrophy Patterns
Individual nail dystrophies include onychoatrophia, anonychia, onychorrhexis, leukonychia, Beau's lines, onycholysis, onychomadesis, onychoschizia, haplonychia, longitudinal melanonychia, and ventral pterygium. 7 Each has distinct clinical descriptions, etiologies, and associated conditions. 7