What are the treatment options for a black toenail?

Black Toenails: Treatment Approach

The treatment of a black toenail depends entirely on the underlying cause—subungual hematoma requires drainage if painful or extensive, fungal infection needs antifungal therapy, and melanonychia warrants urgent evaluation to exclude subungual melanoma. 1, 2

Initial Diagnostic Assessment

The first critical step is determining the etiology of the black discoloration, as this fundamentally changes management:

Subungual Hematoma (Traumatic Blood Collection)

• History of trauma (even minor) with acute onset of dark red-to-black discoloration under the nail plate 3
• The discoloration does not move distally with nail growth and typically resolves as the nail grows out 4
• Immediate drainage is indicated if the hematoma is painful, involves >25% of the nail plate, or causes significant pressure 3

Drainage Technique:

• Use a 29-gauge insulin syringe needle inserted very close to the nail plate near the hyponychium to evacuate blood—this method is faster, simpler, and better tolerated than traditional nail trephining 3
• This technique is particularly successful for smaller hematomas of the second, third, and fourth toenails 3

Fungal Infection (Onychomycosis)

• Gradual onset with thickening, friability, and discoloration (white, green, or black marks) 5
• More common in toenails (80% of dermatophyte infections affect toenails) 5
• Black discoloration can occur with Candida infections, particularly when bacterial superinfection is present 5

Diagnostic Confirmation Required:

• Direct microscopy with potassium hydroxide (KOH) preparation and fungal culture on Sabouraud's glucose agar before initiating treatment 5
• Calcofluor white staining is particularly useful for nail specimens 5

Treatment Options:

• For limited disease (<80% nail involvement, no lunula involvement): Topical amorolfine 5% lacquer applied once or twice weekly for 6-12 months after filing diseased nail areas, with approximately 50% efficacy 5
• For extensive disease: Oral terbinafine 250 mg once daily for 12 weeks for toenail onychomycosis, with mycological cure rates of 70% 6
• Monitor serum transaminases (ALT and AST) before starting oral terbinafine 6

Melanonychia (Melanin Pigmentation)

• Longitudinal band of brown-to-black pigmentation that moves distally with nail growth 1, 2
• Can indicate benign causes (nail matrix nevus, lentigo, post-inflammatory hyperpigmentation) or subungual melanoma 1, 2

Critical Red Flags for Malignancy:

• Irregular borders, color variegation, or rapid changes in the pigmented band 2
• Extension of pigmentation onto the proximal or lateral nail fold (Hutchinson's sign) 5
• New onset in a single digit in adults, particularly in light-skinned individuals 1

Management:

• Nail matrix biopsy is mandatory when melanoma cannot be excluded clinically 5
• This requires a practitioner skilled in nail apparatus biopsy, as melanoma arises in the nail matrix and improper sampling can miss the diagnosis 5
• For suspicious subungual lesions, the nail plate must be sufficiently removed to expose the underlying lesion for excisional or incisional biopsy 5

Bacterial Infection (Pseudomonas)

• Green-to-black discoloration, often with nail fold inflammation 5, 7
• Associated with chronic moisture exposure or paronychia 7

Treatment:

• Keep the affected area dry 7
• Apply topical povidone-iodine 2% twice daily 7, 8
• If paronychia is present with purulent drainage, obtain bacterial culture and consider oral antibiotics (cephalexin or amoxicillin-clavulanate) 8

Common Pitfalls to Avoid

• Never assume a black toenail is "just a bruise" without confirming trauma history—melanoma presenting as melanonychia is frequently overlooked, leading to worse prognosis 1
• Do not treat presumed onychomycosis empirically without mycological confirmation, as clinical appearance alone is unreliable and many non-infectious conditions mimic fungal infection 5
• Avoid superficial shave biopsies for suspected melanoma, as they may underestimate Breslow thickness and miss the diagnosis 5
• Do not use Prussian blue stain to confirm subungual hematoma—it detects hemosiderin, not hemoglobin, and will be falsely negative; benzidine stain is the appropriate histochemical test 4

Follow-Up Considerations

• For treated onychomycosis, optimal clinical effect occurs months after mycological cure due to the time required for healthy nail outgrowth 6
• Clinical relapse rates for toenail onychomycosis are approximately 15% at one year after completing therapy 6
• Any persistent or changing pigmentation warrants re-evaluation to exclude evolving malignancy 1, 2