Adult-onset melanonychia in Indian patients: A comprehensive narrative review

INTRODUCTION

Melanonychia, derived from the Greek words melas (black) and onyx (nail), refers to brown-to-black pigmentation of the nail plate or nail unit, resulting from melanin deposition within the nail keratin.^[1,2] The condition most commonly manifests as a longitudinal pigmented band (melanonychia striata), though diffuse or transverse pigmentation may also occur.^[2,3] This pigmentation arises either from melanocytic activation (increased melanin synthesis by a normal number of melanocytes) or melanocytic hyperplasia (increase in melanocyte number, benign or malignant).^[1,4]

While melanonychia may be mostly benign, particularly amongst individuals with darker Fitzpatrick skin types, its clinical relevance stems from the fact that it may be the earliest sign of subungual melanoma (SUM).^[5,6] Globally, SUM accounts for only 0.7–3.5% of all melanomas, yet it is proportionally more frequent in Asian, African and Hispanic populations and often presents at an advanced stage due to diagnostic delays.^[6-8]

In Indian adults, constitutional and reactive melanonychia (secondary to ethnicity, trauma, inflammation or drugs) is frequently observed.^[9,10] However, delayed recognition of SUM remains a concern, with reported cases being often diagnosed at advanced or metastatic stages.^[11,12] A cultural aversion to nail biopsy, limited access to onychoscopy, and overlapping benign clinical patterns in pigmented skin contribute to this underdiagnosis.^[9,12,13]

Understanding the epidemiology, clinical features and onychoscopic patterns of melanonychia in Indian patients is crucial towards guiding a timely diagnosis and management.

Moreover, emerging molecular data suggest that SUM in Asian populations often harbours KIT (KIT protooncogene, receptor tyrosine kinase) or GNAQ (guanine nucleotide-binding protein, alpha Q polypeptide) mutations rather than the classical BRAF/NRAS (v-raf murine sarcoma viral oncogene homolog B/ neuroblastoma RAS viral oncogene homolog) alterations seen in sun-exposed melanomas, underscoring its distinct pathogenesis and therapeutic implications.^[14-16] This review aims to provide a comprehensive synthesis of adult-onset melanonychia in Indian patients, encompassing its etiopathogenesis, clinical and onychoscopic features, histopathologic and molecular findings, diagnostic approach and management strategies, integrating Indian case series with global evidence.

METHODOLOGY

This narrative review focuses on adult patients with melanonychia, with particular emphasis on data from Indian patients and comparison with global literature. A comprehensive search was conducted in PubMed, Embase, Scopus and Web of Science (2000–2025) using the terms ‘melanonychia’, ‘longitudinal melanonychia’, ‘nail melanoma’, ‘onychoscopy’, ‘nail pigmentation’ and ‘India’. Reference lists were also screened. Articles were included if they reported on adult patients (≥18 years) with melanonychia or nail-unit melanoma (NUM) and contained clinical, onychoscopic, histopathologic or molecular details. Paediatric-only studies, editorials and abstracts without full text were excluded. Given the heterogeneity of data (mostly case reports and small series), findings were synthesised narratively.

EPIDEMIOLOGY

PATHOGENESIS

Longitudinal melanonychia results from two fundamental mechanisms:

• Melanocytic activation (functional)- It involves an increased melanin synthesis and transfer from otherwise normal numbers of matrix melanocytes into the nail plate keratinocytes. Activation may be physiologic (racial/constitutional), hormonally mediated or reactive to local/systemic stimuli.

• Melanocytic hyperplasia (proliferative)- It involves and increased number of melanocytes within the nail matrix epithelium (lentigo, melanocytic nevus) or neoplastic proliferation (subungual/NUM). Histopathology distinguishes activation (increased pigment without increased melanocyte density or atypia) from true hyperplasia.

Large clinicopathologic series and reviews estimate that the majority of LM cases are due to activation (often cited to be 50–75% depending on cohort), while a smaller fraction reflects true melanocytic hyperplasia. The reported malignant yield amongst biopsied longitudinal bands varies by referral population, but remains low overall. As reporting is heterogeneous, precise population-level proportions vary and are influenced by a referral bias (dermatology/oncology centres show higher malignant proportions).^[1,20]

CLINICAL FEATURES

Adult-onset LM may present with various clinical patterns [Figure 1a-c]. A vertical band extending from the proximal fold to the free edge of the nail plate is the most common presentation as well as the most concerning when noticed on a single digit in an adult. Total (diffuse) melanonychia involves an entire nail plate becoming pigmented. Polydactylous total melanonychia is typically associated with systemic causes, whereas monodactylous involvement raises concern for localised pathology, including advanced melanoma.^[35,43,44] Transverse melanonychia is uncommon and most frequently drug-induced.^[1,48]

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Figure 1:

Different types of adult-onset melanonychia. (a) Light brown coloured band of recent onset, involving 4 nails in a 32-year-old male, suggestive of melanocyte activation. (b) Dark coloured band involving a single nail in a 25-year-old female. Progressively darkening for the past 2 years, suggestive of melanocyte proliferation. (c) Broad dark band with progressive colour variegation in a 35-year-old male, arousing suspicion of a malignancy.

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Recognition of red flags in LM is essential for early diagnosis. Benign bands are typically narrow, uniform in colour, stable over time and often involve multiple nails. In contrast, features that raise concern for SUM/NUM include solitary digit involvement (particularly the thumb or great toe), band width exceeding 3 mm, irregular or blurred borders, variegated pigmentation and any rapid change in width or colour. Additional warning signs are the presence of Hutchinson’s sign (pigment extending onto the proximal or lateral nail fold or hyponychium), along with nail plate dystrophy, fissuring, ulceration or bleeding. A personal or family history of melanoma further increases suspicion [Table 1].^[1,3,35] These clinical parameters should be routinely elicited during history and assessed carefully on examination. While the ABCDE rule remains the cornerstone for identifying suspicious cutaneous melanocytic lesions, it does not fully capture the unique presentations of NUM.^[52] To address these differences, the ABCDEF rule was explicitly developed for NUM, incorporating additional parameters such as digit involvement, periungual extension and patient risk factors [Table 2].^[5,53,54] A photographic documentation at baseline and during follow-up (every 3–6 months) is strongly recommended for melanonychia, especially LM.^[9]

Hutchinson’s sign (HS)

Periungual pigmentation, traditionally termed HS, originates from Hutchinson’s 1886 description of ‘melanotic whitlow’ associated with nail melanoma.^[55] Over the years, HS has been considered an important warning sign for SUM; yet its use has often been inconsistent, contributing to its clinical ambiguity. HS is a visible clinical finding, defined as melanin pigmentation on any periungual structure, which should prompt careful evaluation for melanoma [Figure 2a]. Notably, HS may occur in both benign and malignant melanocytic nail lesions.

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Figure 2:

Onychoscopy of longitudinal melanonychia in adult patients. (a) Light brown to grey band with regular edges. Suggestive of melanocyte hyperplasia. (b) Black band with regular edges and peripheral pigment granules, suggestive of melanocyte proliferation (Polarised ×50).

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Pseudo-HS refers to pigmentation visible through the translucent cuticle or proximal nail fold [Figure 2b], while micro-HS denotes subtle periungual pigmentation detectable only on close inspection or onychoscopy. Because periungual pigmentation alone cannot reliably distinguish benign from malignant causes, nail matrix biopsy remains essential for diagnosis in adults. Although descriptive terminology has been proposed, retaining the eponym ‘Hutchinson sign’ is helpful because it alerts clinicians to the possibility of melanoma.^[56] In patients with skin of colour, in whom physiological or racial melanonychia is highly prevalent, benign, faint pigmentation on the nail folds is common. It represents normal melanocyte activation and is not associated with melanoma, affirming that the HS is not pathognomonic for SUM, and its specificity is significantly limited, especially in individuals with skin of colour.

ONYCHOSCOPY

Onychoscopy is an indispensable tool in evaluating pigmented nail bands and guiding biopsy decisions.^[57] Recognition of onychoscopic patterns is crucial for distinguishing benign LM from NUM, particularly in adults presenting with new or changing nail pigmentation. Onychoscopy enhances diagnostic accuracy by allowing detailed assessment of band colour, line regularity, parallelism and periungual pigmentation [Figure 3a-c] – features that often reveal early malignant change before overt clinical signs appear. While benign LM typically demonstrates stable, homogeneous and orderly patterns, NUM is characterised by asymmetry, irregularity and progressive evolution. A comparative summary of key benign versus malignant onychoscopic findings is presented in Table 3.^[57-59]

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Figure 3:

Hutchinson’s sign and its variants. (a) Hutchinson’s sign, seen as a peripheral spread of pigment in the proximal nail fold, in a 22-year-old female. (b) Pseudo-Hutchinson’s sign in a 5-year-old boy. The pigmented band is seen through a transparent cuticle and proximal nail fold. (c) Micro-Hutchinson’s sign on onychoscopy showing pigment spread in the distal nail fold, which was invisible on naked eye examination (Polarised ×50).

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Onychoscopic examination is widely considered the standard-of-care worldwide and can help provide early pointers towards possible malignancy. Its role in the follow-up of these patients is also important. In a Korean series of 8 SUM in situ adult patients, all had presented with a solitary LM with periungual pigmentation in 87.5% cases, along with a pigmented background. As per the authors, the ‘nail ABCD’ rule (Adult age, Brown band in brown background, Colour in periungual skin, single Digit) achieved 100% sensitivity and 96.6% specificity in their series.^[23]

Intra-operative onychoscopy (after removing nail plate) is also useful [Figure 4]. Although operationally difficult, it may show regular parallel matrix pigmentation in benign cases. However, in melanoma, irregular dark structures have been described.^[60]

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Figure 4:

Intra-operative onychoscopy showing regular pigment with defined margins as the matrix origin of a longitudinal pigmented band (Polarised ×50).

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DIAGNOSIS

As outlined above, a detailed history is essential including the age at onset, duration, changes in width/colour, pain/ bleeding, history of trauma, footwear, microtrauma, medications, systemic symptoms (adrenal, endocrine) and family/personal melanoma history. Examination requires review of all nails (fingers and toes) including the number of nails involved, band colour/width, presence of HS or its variants, nail plate changes, symmetry, and condition of adjacent skin/mucosa.^[1-3] If systemic causes are suspected (e.g. adrenal disease, nutritional deficiency), targeted laboratories may include serum cortisol, adrenal panel, B12 levels, iron studies and HIV, as indicated.^[1] If the setting suggests so, FM may be ruled out based on relevant tests.

Any adult with LM showing red-flag features should prompt a nail matrix biopsy. This is especially important in cases where follow-up is not possible. Partial techniques (punch biopsy or incisional biopsy) have a high risk of sampling error; hence, ‘en bloc’ excision of the nail-matrix origin of the band is needed to capture the radial growth phase and any vertical invasion. In pigmented skin types, the threshold for biopsy should be kept low, due to a higher background incidence of benign bands and greater risk of overlooking melanoma.^[1-3,9]

Surgical techniques require removal of the overlying nail plate to expose the matrix origin of the band (the darkest pigmented zone). Adequate sampling of the matrix origin (in toto) is important.^[4] In this regard, tangential excision is very helpful. It is a minimally invasive technique recommended for sampling pigmented nail matrix lesions, particularly those causing LM. This approach allows for sufficient pathological assessment, while minimising the risk of permanent nail plate dystrophy. The procedure involves lifting the proximal nail fold to expose the matrix and removing a thin, superficial layer containing the pigment band origin [Figure 5a-e]. This technique is especially suited for bands wider than 4 mm and is favoured for ruling out melanoma with less post-operative morbidity than full-thickness excision.^[61,62] Pre- and post-operative nail-unit care is essential to minimise dystrophy.

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Figure 5:

Tangential nail matrix biopsy in a case with adult-onset melanonychia. (a) Exposing the matrix origin of the band by retracting the proximal nail fold (held back with stay sutures) and proximal partial avulsion of the nail plate. (b) The matrix melanotic origin is completely defined and then tangentially excised with the blade kept horizontal to the matrix surface. (c) The defect in the matrix as well as the excised melanotic lesion (placed on the gloved finger) can be seen. (d) No trace of melanin in the matrix. (e) The proximal nail fold is released to its original position and sutured on both sides. The sutures can be removed after a week.

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APPROACH TO MELANONYCHIA IN INDIAN ADULT PATIENTS

Table 1 summarises the key features to be evaluated, and findings suggesting benign vs malignant potential in Indian skin. It is intended as a clinical decision aid and not a substitute for biopsy. Any high-risk feature should always prompt a nail matrix biopsy histologic evaluation, which remains the diagnostic gold standard. This is especially important in adult patients in whom follow-up cannot be ensured.

In an adult patient presenting with a recent onset of LM, or a recently expanding band of melanonychia, apart from a detailed history, examination of all 20 nails is mandatory. It should include inspection of all fingers and toes, band width/ colour/border, peri- or lateral fold pigment (HS) or any signs of nail dystrophy. Onychoscopy is essential to evaluate the line pattern, thickness/spacing, background colour and periungual involvement. Baseline photographs (both clinical and onychoscopic) are essential, especially in the scenario where a decision is taken to keep the patient under follow-up.

Assessment of the cause is important. If multiple nails are involved with narrow uniform bands that are stable, it is likely benign (constitutional/reactive). Such cases can be observed with serial onychoscopy every 3–6 months. However, if a solitary digit is involved with a band >3 mm in width, irregular lines/colour, HS, or rapidly changing morphology, it suggests high-risk. With any of these signs, it would be prudent to proceed with nail matrix biopsy from the origin of the band. Partial punch biopsy may suffice only for low-risk cases, but close follow-up is then required.

Thereafter, based on the histologic diagnosis, benign bands may be followed up. Lentigo or nevi require monitoring of the evolution of the band. They may resolve if the excision has been total. Cases diagnosed with dysplasia or melanoma require appropriate treatment [Figure 6]. Surgical management (functional surgery if possible), possible sentinel node staging, adjuvant therapy and surveillance every 3–6 months initially, is required. In Indians, the threshold for biopsy may be higher than in white-skin, given the higher background prevalence of pigmented nails.

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Figure 6:

Structured diagnostic algorithm for adult-onset melanonychia in Indian patients.

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MANAGEMENT STRATEGIES

For adult-onset melanonychia, management is dictated entirely by the underlying histopathologic diagnosis.

PROGNOSIS

The prognosis of adult-onset melanonychia depends on the underlying aetiology. Benign bands carry no specific morbidity apart from cosmetic impact. In SUM, prognosis is stage-dependent. Early (in situ or thin invasive) lesions have favourable outcomes, whereas delayed-stage disease (nodal or distant metastases) carries poor survival. Notably, some studies suggest that SUM may have better overall survival than other acral melanomas, possibly reflecting biological differences, though diagnostic delay remains a key adverse factor. In an Indian case series, metastases were found at presentation in half of the patients. This underscores the negative impact of delayed diagnosis.^[3] Early recognition is critical to improving outcomes.^{[1-3,11,20,66,67]}

CONCLUSION AND FUTURE DIRECTIONS

In Indian patients, adult-onset melanonychia is most frequently benign, reflecting ethnic pigmentation or non-malignant causes. It often requires reassurance and monitoring only. Nonetheless, clinicians must maintain vigilance for SUM, especially when red-flag clinical or onychoscopic features are present. A structured assessment algorithm, incorporating history, full-nail examination, dermoscopy, baseline photography and timely biopsy, provides a pragmatic path to early detection. Emerging molecular data (notably KIT and GNAQ mutations in SUM) highlight that NUM may represent a biologically distinct entity compared to sun-exposed cutaneous melanoma; however, Indian-specific molecular data are lacking. Further research in India on prevalence, onychoscopic patterns, histopathologic correlates and genetic drivers of nail-unit melanonychia and melanoma is strongly needed. Given the cultural and resource-related factors that may delay diagnosis (reluctance for biopsy, nail-cosmetic concerns, misdiagnosis as fungal infection/trauma), increasing clinician awareness, improving access to dermoscopy and judicious use of biopsy in suspicious cases will help shift outcomes favourably.