Inflammatory Nail Disorders in Skin of Color: A Systematic Review of Clinical and Onychoscopic Manifestations

ABSTRACT

Despite increasing attention regarding skin diseases in individuals with skin of color (SoC), there remains a significant gap in understanding and identifying inflammatory nail disorders in this population. This systematic review aims to synthesize the clinical and onychoscopic features of inflammatory nail disorders in patients with SoC, thereby enhancing diagnostic accuracy and patient outcomes. Our systematic PubMed and Medline (Web of Science) search followed PRISMA guidelines. Studies documenting clinical and onychoscopic features of inflammatory nail disorders in Fitzpatrick skin types IV–VI were included. Data extraction focused on study design, patient demographics, diagnostic methods, and nail findings. Of the 608 articles identified, 60 met the inclusion criteria, encompassing 16 inflammatory nail disorders and 12,743 patient cases. Key disorders included nail psoriasis, nail lichen planus, alopecia areata‐associated nail changes, and others. Significant variability was noted in reporting skin type, with only a minority explicitly documenting SoC representation. This review underscores the paucity of literature on inflammatory nail disorders in SoC, highlighting gaps in clinical documentation and diagnostic approaches. Improved awareness and inclusion of SoC in dermatologic research are critical to addressing these disparities and enhancing health equity. Recognition of diverse clinical presentations in SoC patients is essential for accurate and timely diagnosis of inflammatory nail disorders. PROSPERO number: CRD42024568649.

1. Introduction

Despite growing efforts to explore skin diseases in individuals with skin of color (SoC) [1], a significant gap remains in understanding nail disorders in this population. Inflammatory nail disease is common in clinical practice [2]; however, it contributes significantly to patient morbidity [3] and quality of life [4, 5]. For instance, SoC patients with nail psoriasis (NP) often experience longer times to diagnosis and present with more severe disease [6]. Notably, NP is associated with more than just skin disease; it is a diagnostic criterion for psoriatic arthritis (PsA) according to the Classification of Psoriatic Arthritis (CASPAR) Study Group criteria [7]. Thus, failure to promptly recognize NP can lead to delays in diagnosing and treating PsA, further exacerbating patient outcomes [7].

This systematic review aims to synthesize the clinical and onychoscopic features of several inflammatory nail disorders in patients with SoC. This review seeks to improve overall awareness, diagnostic accuracy, and treatment outcomes by providing a comprehensive analysis, ultimately contributing to diagnostic advancements and better health equity [8, 9]. To our knowledge, this is the first systematic review to focus specifically on these disorders in SoC.

2. Methods

On June 20, 2024, a systematic search of PubMed and Medline (Web of Science) was conducted in accordance with PRISMA guidelines and was registered with PROSPERO (CRD42024568649). The search terms employed to identify articles documenting clinical and onychoscopic features of inflammatory nail disorders in SoC are outlined in Table S1. This literature search yielded 608 articles.

Two researchers (L.T. and J.T.) independently reviewed titles and abstracts to remove duplicates and abstract‐only reports. A total of 509 full‐text articles were accessed for eligibility. Exclusion criteria included nonrelevant, non‐English, and non‐accessible articles, and those without recorded clinical or onychoscopic findings. The Fitzpatrick skin phototype (FSP) scale was utilized to classify SoC (defined as Fitzpatrick IV–VI) in this review, as it was the only method employed for classifying skin type among the included studies and serves as a widely recognized reference for clinicians. Photographs not classified by skin type by the original authors were assessed and categorized according to the FSP scale. When articles lacked written or photographic evidence of skin phototype, author and patient cohort origin were evaluated to optimize SoC inclusion.

A total of 60 articles were included in the final review. The PRISMA flowchart is provided (Figure 1). Data extraction included the study design, author and patient cohort origin, skin phototype, and method for classification, diagnosis, and clinical and onychoscopic features.

FIGURE 1.

PRISMA flowchart displaying the selection process for study inclusion.

3. Results

Of the 509 articles identified, 60 studies were included in the final analysis. Table S2 outlines the characteristics of these studies. Study designs included 19 cross‐sectional, one case–control, five retrospective, six prospective, and two cohort studies; 21 case reports; four case series; and two reviews with photographic case reports.

Documentation of skin phototypes by original authors was provided in 3 of 60 (5.0%) records. In 23 articles (38.3%), there was neither written nor photographic evidence of skin phototype. Therefore, the country of origin of the authors and patient cohort was considered. Among these articles, 14 originated from India and included Indian patient cohorts, two from Nigeria, two from Malaysia, one from Thailand, three from Malaysia/China/India, and one from Iran. Of the articles reviewed, 35 (58.3%) were identified as relevant to the SoC population based on our assessment of the published images, which the original authors had not classified.

Sixteen inflammatory nail disorders were identified, encompassing 12,743 patient cases. These included NP; nail lichen planus (NLP); nail lichen nitidus (NLN); nail lichen striatus (NLS); parakeratosis pustulosa (PP); acute and chronic paronychia (AP and CP, respectively), trachyonychia, also known as twenty nail dystrophy (TND); onychotillomania; and nail changes associated with alopecia areata (AA), vitiligo, pityriasis rubra pilaris (PRP), pityriasis rosea (PR), pityriasis lichenoides chronica (PLC), atopic dermatitis/eczema (AD), and parapsoriasis. Table S3 outlines the clinical and onychoscopic features, further classified by nail bed, nail plate/matrix, and nail fold findings, observed in each reported inflammatory nail disorder.

4. Discussion

4.1. Nail Psoriasis

Individuals of racial and ethnic minorities are typically diagnosed with NP almost three years later than their non‐SoC counterparts, often presenting with more severe symptoms [6]. Diagnosing psoriasis in darker skin types presents challenges. For instance, erythema may be less pronounced, appearing violaceous or hyperpigmented, frequently leading to misdiagnosis, such as other papulosquamous disorders and delayed diagnosis [10]. Longitudinal melanonychia and darker nail beds can obscure typical signs of NP, such as onycholysis and pitting. In our review, NP was observed in 11,851 (93.0%) patients (Figure 2).

FIGURE 2.

(a) Nail psoriasis. Fingernails with hyperpigmentation of the proximal nail folds, thin longitudinal dark bands, distal onycholysis, subungual hyperkeratosis, brown‐red discoloration proximal to the areas of onycholysis, and scattered pits. (b) Dermoscopic image of nail psoriasis. Fingernail with hyperpigmentation of the proximal nail folds, several thin longitudinal gray bands, distal onycholysis, brown discoloration proximal to the areas of onycholysis, and splinter hemorrhages.

4.2. Nail Findings in Alopecia Areata

Although nail involvement is not always present in AA, it occurs more frequently in severe forms of the disease, such as alopecia totalis and alopecia universalis, and is considered a negative prognostic factor [4]. The literature addressing clinical features and diagnosis of AA‐associated nail changes, particularly among patients with SoC, is notably sparse [11].

Our systematic review included 329 patients (2.58%) with documented nail involvement associated with AA. Common AA‐related nail findings, including pitting, onychorrhexis, and trachyonychia, were also observed in our SoC cohort (Table S3) [11, 12]. Histopathologically, AA‐associated nail disease is primarily a disorder of proximal nail matrix keratinization, with limited involvement of the distal matrix and fewer nail bed changes [11]. Moreover, these nail plate changes are a significant manifestation of AA, independent of skin color, and may be more readily recognized when compared to nail bed changes on examination of SoC patients. Onychoscopic features were not reported in the included studies.

4.3. Nail Findings in Atopic Dermatitis

Patients with SoC are disproportionately affected by AD, experiencing greater disease prevalence and severity [13]. Despite well‐documented cutaneous manifestations, nail involvement in AD remains poorly understood, particularly in SoC patients [14]. Studies highlight prevalent AD‐related nail changes, including pitting, trachyonychia, melanonychia, onycholysis, and onychomadesis [14, 15, 16]. Notably, higher AD severity, as measured by SCORAD (SCORing Atopic Dermatitis), is strongly associated with nail pitting and trachyonychia [14].

Our systematic review identified three articles encompassing a total of 270 SoC patients (2.12%) with AD‐associated nail changes. The predominant findings were “shiny nails” (81.9%), indicative of shiny trachyonychia characterized by uniform, opalescent nails with reflective pits [17] and pitting (17.7%) (Table S3). These results are particularly interesting given their correlation with severe AD, likely reflecting the propensity for a greater disease burden in SoC patients [13].

4.4. Nail Lichen Planus

NLP is a benign inflammatory disorder of unknown etiology that can cause profound functional and quality of life impairment [18]. The potential development of a disappearing nail bed, anonychia, or pterygium, and irreversible scarring of the nail matrix indicating advanced disease highlight NLP as a true nail emergency [19, 20]. Thus, early diagnosis and treatment of NLP are crucial in patients of all skin types [20].

NLP was observed in 117 (0.92%) patients. Clinical features commonly reported in NLP, including longitudinal ridging/splitting, onychorrhexis, nail plate thinning, onycholysis, and subungual hyperkeratosis [18, 21], were similarly identified in our SoC cohort (Table S3). Notably, longitudinal melanonychia was observed in 12.3% of clinical exams and 12.7% of onychoscopic evaluations. While frequently physiological in individuals with ethnic skin and induced by melanocyte activation in the setting of inflammatory nail diseases [22], longitudinal melanonychia can obscure other features of NLP, particularly in darkly complected patients [23]. This can lead to misinterpreted clinical examinations, delayed diagnosis, and disease progression, resulting in irreversible nail changes. Moreover, permanent nail scarring, including pterygium and anonychia, was documented in 59 instances, reinforcing the urgency for prompt and precise diagnosis and management across all patient demographics (Figure 3).

FIGURE 3.

Nail lichen planus. Fingernails with fissuring and splitting of the nail plate, distal onycholysis, and a thin red onychodermal band.

4.5. Acute and Chronic Paronychia

Paronychia, an inflammatory condition of the proximal and/or lateral nail folds, manifests in both acute and chronic forms [24]. Acute paronychia (AP), lasting less than 6 weeks, typically arises from bacterial infections following inciting nail trauma, such as onychophagia, manicures, or penetrating injuries [25]. Importantly, noninfectious causes include conditions like pemphigus vulgaris, pustular psoriasis, and reactive arthritis, and certain medications, such as epidermal growth factor receptor inhibitors, cytotoxic chemotherapies, and antiretroviral drugs [25], which should be considered in treatment‐refractory or difficult‐to‐treat cases.

Chronic paronychia (CP) is increasingly recognized as a form of hand eczema, driven primarily by prolonged exposures to moisture and environmental irritants [24]. This causes repeated inflammation, leading to persistent edema, induration, fibrosis, and eventually retraction of nail folds with loss of vascular supply [26]. This cyclic progression complicates treatment and may reduce the effectiveness of topical medications [24].

In our review, CP affected 94 (0.74%) patients, while AP and unspecified paronychia were reported in 10 (0.08%) and 15 (0.12%) cases, respectively. Common presentations for both AP and CP include nail fold erythema and swelling, both of which were consistently observed in this SoC patient cohort (Table S3). However, in the absence of apparent erythema, other diagnostic insights for identifying paronychia in darker skin types include nail fold and plate discoloration or hyperpigmentation and changes in the cuticle, such as separation, retraction, or absence.

4.6. Trachyonychia and Twenty Nail Dystrophy

Trachyonychia is a disorder of the nail that may manifest as an idiopathic condition or in the setting of several inflammatory disorders, including psoriasis, LP, and AA [17, 27]. It is characterized by two distinct presentations: opaque trachyonychia, marked by rough, longitudinally ridged nails, and shiny trachyonychia [17]. Opaque trachyonychia is thought to result from a persistent, waxing and waning inflammatory insult to the nail matrix, whereas shiny trachyonychia is marked by intermittent, focal inflammatory insults interspersed with periods of normal matrix function [28], contributing to their distinct clinical presentations.

Our review reported trachyonychia and twenty nail dystrophy (TND)—or trachyonychia involving all 20 nails—in 16 patients (0.13%) and 1 patient (0.01%), respectively. Trachyonychia was reported in a single study; however, no clinical findings were documented (Table S3). Similar to changes associated with AA, the characteristics of trachyonychia and TND may be more equally recognized in patients with darker skin types, owing to the prominence of nail plate alterations in comparison to nail bed changes. As such, longitudinal ridging/onychorrhexis, onychodystrophy, and brittle nails were the most frequently reported onychoscopic findings in SoC patients (Table S3).

4.7. Onychotillomania

Onychotillomania, or nail‐picking disorder, is a rare and often misdiagnosed behavioral condition characterized by a compulsive urge to damage the nail apparatus [29, 30]. This self‐injurious behavior can lead to significant and sometimes irreversible damage to the nail unit, creating substantial diagnostic and therapeutic challenges due to both the variability of clinical presentations and the frequent patient denial of nail manipulation [29, 30].

Onychotillomania was observed in 16 patients (0.13%). The most frequent clinical manifestation was longitudinal melanonychia (40%), followed by Beau's lines, nail plate discoloration with sparing of a single digit, and absent cuticles, each noted at a frequency of 20% (Table S3). Onychoscopic findings revealed nail bed pigmentation and the absence of the nail plate in 14 patients (50%) each (Figure 4).

FIGURE 4.

(a) Onychotillomania. Fingernails with anonychia, grayish‐brown nail bed hyperpigmentation, and ragged cuticles. (b) Dermoscopic image of onychotillomania. Fingernails with wavy nails associated with nail bed hyperpigmentation, linear nail bed erythema and telangiectasia, and proximal nail fold dystrophy.

4.8. Nail Findings in Pityriasis Rubra Pilaris

Diagnosing PRP can be challenging in patients with darker skin phototypes due to less conspicuous skin manifestations, which may appear more violaceous or hyperpigmented than the classic orange or salmon‐colored rash [31]. Thus, recognition of nail changes may enhance diagnostic accuracy, particularly in SoC patients [31].

Nail changes associated with PRP were reported in eight patients (0.06%). Among NP and PRP, there were multiple overlapping findings; however, a few unique features of PRP were reported, including onychoschizia, koilonychia, and ragged cuticles (Table S3). Additionally, nail plate thickening and subungual hyperkeratosis were clinically more prevalent in PRP (23.8% each) than in NP (0.13% and 10.6%, respectively). Although not observed in this SoC cohort, distal yellow‐brown discoloration and splinter hemorrhages have also been reported as additional findings supporting a diagnosis of type 1 PRP rather than NP [32].

4.9. Nail Lichen Nitidus

Nail lichen nitidus (NLN) is often underrecognized and can precede cutaneous lesions [33], leading to delayed diagnosis due to its rarity and subtle presentation. Though cases of nail changes in LN are documented, reports are limited [34], particularly among patients with SoC. Nail involvement in LN occurs in approximately 10% of cases and generally presents alongside palmar involvement [35]. Described nail changes associated with LN include longitudinal ridging, pitting, nail plate thickening, trachyonychia, onycholysis, and nail fold involvement with periungual inflammation and violaceous shiny papules [36, 37]. Seven (0.05%) patients with NLN were included in our review. The most common clinical findings in this SoC cohort included unspecified leukonychia (13.6%), longitudinal ridging (13.6%), onychodystrophy (13.6%), nail plate thinning (9.1%), and nail fold darkening (9.1%) (Table S3).

The co‐occurrence of LN with LP in up to 30% of cases suggests that these may represent different manifestations of the same underlying process rather than distinct entities, although they are histopathologically different [38]. This is particularly relevant given the higher prevalence of LP among white (61%) and black (23%) populations in the United States compared to other racial and ethnic groups [39]. Importantly, NLN differs from NLP in that it does not carry a risk of progression to permanent nail scarring, thus influencing management and prognosis.

4.10. Nail Lichen Striatus

Lichen striatus (LS) is a rare and self‐limiting dermatosis characterized by asymptomatic, linear lesions typically following Blaschko's lines [40]. Although primarily a cutaneous condition, various nail changes can arise when the linear eruption extends to the periungual area [41]. Nail involvement in LS is relatively infrequent and may occur independently of skin lesions [41]. Due to the rarity of NLN, there is limited literature detailing its characteristic features. Nevertheless, longitudinal ridging and fissuring, onycholysis, subungual hyperkeratosis, splitting, and partial or complete loss of the nail plate have been previously described [40, 41, 42].

Four patients (0.03%) with SoC and a reported diagnosis of NLS were included in this review. Clinical findings reported in this SoC population included longitudinal ridging and striations, nail plate thinning, and splitting (27.3% each). All clinical and onychoscopic features are outlined in Table S3.

4.11. Nail Findings in Other Inflammatory Nail Diseases

PP is a rare dermatosis primarily affecting children under five, with a higher prevalence in females [43]. It is characterized by vesiculopustular lesions localized to the hyponychium, often extending into the distal nail bed with subsequent nail changes, including onycholysis [44]. PP typically presents as single‐digit involvement and is generally asymptomatic [43]. In this review, two patients (0.02%) with PP were identified. Both patients exhibited clinical signs of onycholysis (Table S3). Among other findings, erosive pustules along the hyponychium and nail folds, subungual hyperkeratosis, longitudinal ridging, and nail plate thinning were noted in individual patients (Table S3).

PR, a common papulosquamous dermatosis primarily affecting children and young adults, has been linked to human herpesvirus (HHV)‐7 and HHV‐6, although its precise etiology remains undefined [45]. In our review, PR with associated nail changes was observed in two patients (0.02%). Both cases exhibited clinical and onychoscopic evidence of Beau's lines (2, 100%) (Table S3). Beau's lines, or transverse grooves within the nail plate, are caused by a temporary disruption in the growth of the proximal nail matrix [46]. While most commonly associated with acute systemic illness and chemotherapeutic agents, Beau's lines affecting multiple fingers have been reported following viral infections, including coronavirus disease 2019 and coxsackievirus hand‐foot‐mouth disease [47, 48, 49, 50]. However, since nail involvement in PR is rarely documented, these findings may be incidental rather than characteristic of the disease (Figure 5).

FIGURE 5.

Beau's lines. Fingernails with Beau's lines in a patient with pityriasis rosea.

In contrast, pityriasis lichenoides represent a distinct group of inflammatory skin disorders, including PLC, for which the pathophysiology remains unclear [51]. Several pathogenic hypotheses have been proposed, including an inflammatory response secondary to infectious agents or drugs, an inflammatory reaction due to T‐cell dyscrasia, and immune‐complex‐mediated hypersensitivity vasculitis [52]. Pathogens such as human immunodeficiency virus (HIV), varicella zoster virus (VZV), Epstein–Barr virus (EBV), parvovirus B19, and certain bacteria have been associated with PLC [52]. Despite its potential connections to infectious agents, reports of nail involvement in PLC are exceedingly rare across all skin types [53]. Our analysis identified only one patient (0.01%) with documented nail changes, specifically Beau's lines (Table S3).

Parapsoriasis encompasses a group of rare, chronic, and persistent inflammatory skin diseases of unknown etiology [54]. Among its subtypes, large plaque parapsoriasis (LPP) can potentially progress to cutaneous lymphoma, particularly mycosis fungoides [54]. Reports of nail involvement in parapsoriasis are exceedingly rare [20]. In our analysis, we identified one patient (0.01%) with parapsoriasis who exhibited Beau's lines (Table S3). Similar to our findings in PR and PLC, the presence of Beau's lines in this patient is likely coincidental rather than directly associated with the condition, given the limited number of documented cases.

Our review highlighted the distinctive features of inflammatory nail disorders in patients with SoC. Longitudinal melanonychia and nail plate discoloration were prevalent across various conditions, such as NP, NLP, and onychotillomania. This type of reactive melanonychia, indicative of melanocyte activation due to inflammatory changes, is relatively uncommon in lighter skin types [55] and should be a diagnostic consideration in SoC patients. Specifically, longitudinal melanonychia was a prominent feature of NLP, whereas nail plate discoloration was frequently reported in NP and paronychia.

Furthermore, onycholysis and subungual hyperkeratosis were predominant nail bed findings in NP, while classic signs in lighter skin, such as salmon patches or red onychodermal bands, were scarcely reported. This disparity likely stems from the challenge of detecting nail bed erythema in individuals with darker skin tones, highlighting the importance of reporting and recognizing distinct nail presentations in SoC patients.

The FSP scale was selected to classify SoC in this review and maintain internal consistency with the included studies. Notably, this scale was not employed to estimate clinical risks (i.e., skin cancer risk) based on skin type; instead, it serves as a familiar and widely recognized framework for identifying SoC, reflecting its current prevalence in clinical practice and research [56]. Nevertheless, we acknowledge that the FSP scale, originally designed to assess response to ultraviolet exposure, does not fully capture the complexity and diversity of SoC across various populations.

Recognizing these limitations underscores the need for a comprehensive and validated skin classification tool tailored for clinical assessments within diverse populations. Future studies may benefit from incorporating skin colorimeters to obtain objective measurements of pigmentation and color, providing more consistent and reliable data than the FSP scale.

5. Conclusion

To our knowledge, this is the first systematic review to specifically investigate the clinical and onychoscopic features of inflammatory nail disorders in patients with SoC. Our findings highlight significant gaps in the literature, with only a small proportion of studies explicitly documenting skin phototypes or providing sufficient visual evidence to classify skin color. Among the 60 articles included in this review, only three explicitly documented skin phototypes, and many relied on the country of origin of authors and patient cohorts to infer SoC representation.

Despite these limitations, the review identified 16 inflammatory nail disorders, encompassing 12,743 patient cases, with specific clinical and onychoscopic features documented for conditions such as NP, NLP, AA, AD, and others. Longitudinal melanonychia and nail plate discoloration, commonly reported in NP and NLP, are not typical in lighter skin types (Fitzpatrick I–III) [57], indicating that melanonychia is a more frequent finding in inflammatory nail disorders among individuals with SoC. Subungual hyperkeratosis and onycholysis were also frequently reported in NP, in contrast to salmon patches and other erythematous changes commonly observed in lighter skin [57]; these findings were rarely noted in our review. These findings underscore the complexity of diagnosing nail disorders in SoC, where clinical signs may differ or be less pronounced, leading to potential delays in diagnosis and treatment.

This review supports the need for increased representation of SoC in dermatologic research and clinical documentation. By providing a comprehensive summary of the existing data, we aimed to bridge the knowledge gap and encourage more inclusive research practices. Enhanced awareness and understanding of inflammatory nail disorders in SoC will improve diagnostic accuracy, treatment outcomes, and overall health equity.

Consent

Consent was obtained from all patients whose photographs are included.

Conflicts of Interest

Dr. Tosti is a consultant for DS Laboratories, Almirall, Thirty Madison, Eli Lilly, Bristol Myers Squibb, Pfizer, Myovant, Ortho Dermatologics, and Concert; none are related to this manuscript. Author Tordjman, Dr. Thomas, and Dr. Morrison have no conflicts of interest to declare.

Supporting information

Table S1. Search terms used in PubMed and Medline (Web of Science).

Table S2. Summary of 60 included articles, inflammatory nail disorder and patient characteristics.

Table S3. Inflammatory nail disorders with associated clinical and onychoscopic features and their frequencies.