What causes unilateral downward-growing fingernails (onychogryphosis) on one hand?

Unilateral Downward-Growing Fingernails: Diagnostic Approach

Unilateral downward-growing fingernails (onychogryphosis) affecting only one hand suggests an acquired condition related to localized trauma, vascular compromise, neurological impairment, or chronic infection rather than a systemic or congenital cause. 1, 2

Key Distinguishing Features of Unilateral Presentation

The unilateral nature is the critical diagnostic clue here:

• Acquired onychogryphosis typically affects a single nail or one extremity, distinguishing it from congenital forms which affect all fingers and toenails bilaterally 2
• Trauma history is paramount - look specifically for previous crush injuries, repetitive occupational trauma, or chronic pressure to the affected hand 3, 2
• Vascular insufficiency affecting one limb can cause nail dystrophy with thickening and abnormal growth patterns 2
• Neurological disorders affecting one side (stroke, peripheral nerve injury, hemiplegia) may result in unilateral nail changes due to altered sensation and self-care ability 2

Essential Clinical Evaluation

Examine the affected hand for:

• Associated skin changes - look for tinea pedis/manuum, psoriatic plaques, or lichen planus, as fungal infection is present in over 90% of nail dystrophies and can cause secondary nail plate thickening 4
• Vascular status - assess capillary refill, temperature, and pulses comparing both hands, as peripheral circulation disorders are strongly associated with onychogryphosis 2
• Neurological function - test sensation and motor function, as central nervous system diseases can lead to unilateral nail neglect and secondary dystrophy 2
• Joint deformities - check for arthritis or finger malalignment that could cause chronic pressure on specific nails 2

Diagnostic Workup

Fungal infection must be ruled out first because it is the most common treatable cause:

• Obtain nail clippings from the discolored, dystrophic areas for potassium hydroxide (KOH) preparation and fungal culture on Sabouraud's glucose agar 4, 5
• Fungal infections present with thickening, discoloration, and friable texture, and dermatophyte infection (primarily Trichophyton rubrum) causes over 90% of onychomycosis cases 4
• Nondermatophyte moulds should be suspected when previous antifungal treatment has failed, direct microscopy is positive but no dermatophyte grows, and only one nail is affected 4

Management Algorithm

Step 1: Treat confirmed fungal infection if present

• Terbinafine is the preferred systemic antifungal for fingernail onychomycosis, given for 6 weeks at 250 mg daily (for adults >40 kg) 4
• Only treat after mycological confirmation - do not prescribe antifungals empirically 5

Step 2: Address mechanical factors

• Daily application of urea-based keratolytic cream to reduce nail plate thickness 5
• Gentle filing with an emery board after softening nails in warm water 5
• Consider mechanical debridement or partial nail avulsion for severe cases causing pain or functional impairment 4

Step 3: Investigate underlying systemic causes

• Evaluate for diabetes, peripheral vascular disease, or neurological conditions if no clear traumatic or infectious etiology is identified 2
• The unilateral presentation in an otherwise healthy patient strongly suggests localized rather than systemic pathology 1

Critical Pitfalls to Avoid

• Do not assume fungal infection without laboratory confirmation - many conditions mimic onychomycosis including psoriasis, chronic trauma, and lichen planus 4
• Do not overlook occupational or habitual trauma - repetitive use of one hand for specific tasks can cause isolated nail dystrophy 2
• Do not miss vascular insufficiency - particularly in patients with diabetes or smoking history, as onychomycosis is a significant predictor for foot ulcers in diabetics 4
• Chronic paronychia can cause proximal nail dystrophy with ridging in patients with wet occupations or chronic moisture exposure, and affects the nail matrix area 5

Preventive Measures

• Apply daily topical emollients to periungual folds and nail matrix to maintain hydration 5
• Avoid trauma, nail biting, and use of nails as tools 5
• Wear protective gloves when working with chemicals or in wet environments 5, 6
• Address footwear issues if toenails are also affected, as improper footwear pressure contributes to onychogryphosis 2