The hallmark symptom is a single pigmented stripe within the nail plate. The band may be light tan or very dark, and it may remain stable or change over time. Common features include:

• A vertical pigmented band that extends from the nail matrix area near the cuticle to the free edge
• Pigmentation affecting one nail or multiple nails
• A band that is narrow and uniform or wider with varying shades
• Changes over time, including darkening, widening, or irregular borders
• Pigment that appears to extend onto surrounding skin at the cuticle or sidewalls
• Nail surface changes such as splitting, brittleness, or distortion in some cases
• Associated tenderness or history of repeated trauma, especially in toes

While many presentations are harmless, concerning patterns include a band that becomes progressively wider, develops irregular color variation, or is accompanied by new nail dystrophy. Prompt assessment is recommended when any of these changes occur.

Longitudinal melanonychia (nail discoloration) occurs when melanin pigment is incorporated into the nail plate as it grows. This can happen due to melanocyte activation (existing pigment-producing cells create more pigment) or melanocyte proliferation (an increased number of pigment-producing cells). Potential causes include:

• Physiologic pigmentation: Benign pigment bands can occur as a normal variant, particularly when multiple nails are involved.
• Trauma or repetitive friction: Sports, tight footwear, manicure-related injury, nail biting, and repetitive tapping can stimulate pigment changes in the nail unit.
• Medications: Certain medications can cause nail pigmentation, sometimes affecting several nails.
• Inflammation or infection: Some inflammatory nail disorders and certain infections can contribute to pigment changes.
• Benign melanocytic lesions: A benign nail matrix nevus can create a stable band, often present for a long period.
• Nail unit melanoma: Although uncommon, melanoma can present as longitudinal melanonychia (nail discoloration), especially when one nail is affected and the band changes in width or irregularity over time.

Because multiple causes look similar at first glance, a structured dermatology evaluation is important for distinguishing benign conditions from those requiring biopsy.

Diagnosis begins with a detailed history and nail examination. Dr. Thomas Knackstedt and the Peak Skin Center team typically evaluate:

• Onset and timeline: When the band first appeared and whether it has changed
• Number of nails involved: Single-nail involvement versus multiple-nail involvement
• Band characteristics: Width, color uniformity, border regularity, and location within the nail
• Associated features: Nail splitting, dystrophy, pain, recent trauma, or pigment beyond the nail
• Risk factors: Personal or family history of skin cancer, immunosuppression, or other relevant medical history
• Medication review: New or long-term medications that could contribute to pigmentation

A magnified nail exam (often called onychoscopy or dermoscopy of the nail) may be used to assess pigment patterns more precisely. When the appearance is suspicious or the diagnosis remains uncertain, a nail matrix biopsy may be recommended. Biopsy is the definitive method to clarify the cause of longitudinal melanonychia (nail discoloration) and to evaluate for nail unit melanoma when warranted.

Treatment depends on the underlying cause and the level of clinical concern.

• Observation and monitoring: If findings strongly suggest a benign cause, management may involve documentation with measurements and photographs and follow-up examinations to confirm stability over time.
• Trigger reduction: When trauma or friction is suspected, reducing mechanical stress (footwear modifications, activity adjustments, nail-care changes) may help prevent progression.
• Medication-related management: If medication effects are suspected, the care plan may include coordination with the prescribing clinician when appropriate, recognizing that medication changes are not always possible or necessary.
• Treatment of contributing nail disease: If inflammation or infection is identified, targeted therapy may be recommended.
• Biopsy-directed care: If biopsy is performed, next steps are guided by the results. Benign findings may require no further treatment or may lead to continued monitoring.
• Referral and coordinated care for malignancy: If nail unit melanoma is diagnosed, management typically involves surgical care and may include coordination with appropriate specialists based on disease extent.

The primary goal is an accurate diagnosis with timely intervention when needed, while avoiding unnecessary procedures when a benign pattern is clearly supported.