Longitudinal erythronychia (LE) presents as a red or pink band that runs down the length of the nail plate, originating near the cuticle and extending to the free edge. This visible streak reflects a change occurring in the underlying nail unit tissue, specifically the nail matrix or nail bed. While the appearance of a persistent red line on a fingernail or toenail can be concerning, the potential severity varies widely depending on the underlying cause. This article clarifies the conditions that result in this presentation and explains why medical evaluation is necessary to determine the streak’s nature.
Defining Longitudinal Erythronychia
Longitudinal erythronychia is a descriptive term for a linear red, pink, or reddish-brown discoloration in the nail plate. This streak is the result of a localized process affecting the tissue that forms or supports the nail, known as the nail matrix and nail bed. The color is caused by blood vessels becoming more visible through the nail (erythema) or by a small amount of bleeding.
The appearance can range from a fine, faint line to a wide, prominent band. LE is classified based on the number of digits involved: localized LE affects one nail, while polydactylous LE involves multiple nails. A single streak often suggests a localized issue, such as a tumor, while multiple streaks frequently suggest an underlying systemic or inflammatory condition.
Common Benign Sources of the Red Streak
The majority of longitudinal erythronychia cases are caused by benign conditions.
Benign Tumors
The most common cause of a single, localized red streak is a benign tumor called an onychopapilloma. This small growth in the distal nail matrix or nail bed causes a localized defect, leading to a thinner section of the nail plate, which makes the underlying vascular tissue appear redder.
Another common benign tumor is a glomus tumor, which often presents as a localized red or bluish nodule beneath the nail. These tumors are characterized by intense, paroxysmal pain, extreme sensitivity to cold, and localized tenderness when pressed. The vascular nature of the glomus body accounts for both the discoloration and the characteristic pain.
Inflammatory Conditions
Inflammatory skin diseases frequently cause erythronychia, particularly when multiple nails are involved. Lichen planus, a condition causing inflammation in the skin and mucous membranes, can affect the nail matrix, resulting in one or more red streaks, often alongside thinning of the nail plate. Darier disease, a genetic disorder affecting skin cells, also commonly presents with polydactylous LE, sometimes described as alternating red and white “candy-cane” stripes. These conditions require management of the underlying disease but are not malignancies.
Identifying Malignant Potential
A single, persistent red streak can be a sign of localized malignancy, necessitating prompt medical evaluation. Malignant conditions presenting as LE include Subungual Squamous Cell Carcinoma (SCC) and, less frequently, amelanotic Subungual Melanoma (SUM). Amelanotic melanoma is particularly concerning because it lacks the typical brown or black pigment associated with most melanomas, appearing pink or red instead.
Practitioners rely on an adaptation of the ABCDEF rule to differentiate concerning lesions from benign ones. Suspicion should be raised by a widening of the red band, a change in its color (variegation or darkening), or a blurring of the borders. Involvement of the surrounding skin, known as Hutchinson’s sign, where the redness extends onto the proximal or lateral nail fold, strongly indicates a potential malignancy.
Additional warning signs include the streak’s presence on the thumb or big toe (digits most commonly involved in SUM) or a history of the lesion changing rapidly. Patients over the age of 50 presenting with a new, single red band should be evaluated promptly to rule out SCC or amelanotic melanoma.
The Medical Diagnostic Process
A medical specialist, typically a dermatologist, begins the diagnostic process by examining the nail and taking a detailed patient history. Non-invasive tools, such as dermoscopy (also called onychoscopy), are used to examine the streak with magnification and specialized lighting. Dermoscopy allows the clinician to visualize micro-features of the nail unit, such as the pattern of blood vessels or the presence of subtle pigmentation, providing clues about the streak’s origin.
A definitive diagnosis often requires a small surgical procedure. A nail matrix biopsy is performed when clinical or dermoscopic features suggest malignancy or when the diagnosis remains uncertain. The procedure involves numbing the digit and removing a small piece of nail matrix or nail bed tissue for microscopic analysis.
For longitudinal erythronychia, a longitudinal excision is often the preferred biopsy technique. This method samples the entire length of the pathology, from the matrix to the nail bed, confirming whether the process is benign, inflammatory, or malignant. While a biopsy carries a small risk of permanent nail dystrophy, it is a necessary step when malignancy is suspected.
Treatment Approaches Based on Cause
The management plan for longitudinal erythronychia depends entirely on the final diagnosis confirmed by the biopsy. For benign causes, such as a stable onychopapilloma, treatment is often observation with periodic follow-up to monitor for any changes in the band. Symptomatic benign tumors, like a painful glomus tumor, are treated with simple surgical excision to remove the growth and resolve discomfort.
If the erythronychia results from an inflammatory disease like lichen planus, treatment focuses on managing the underlying condition, often using topical or injected anti-inflammatory medications. For confirmed malignancy, such as Subungual Squamous Cell Carcinoma or Melanoma, the approach is surgical and focuses on complete tumor removal. This may involve wide local excision of the nail unit or, in advanced cases, partial or complete amputation of the affected digit. Early detection through prompt evaluation is the most important factor for a positive outcome.