Comparison of clinical and dermoscopical nail findings of rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis and psoriasis: A prospective study

Abstract

Psoriasis (PsO), psoriatic arthritis (PsA), rheumatoid arthritis (RA), and ankylosing spondylitis (AS) are chronic inflammatory disorders classified as immune-mediated inflammatory diseases (IMIDs). Although these diseases share common pathogenic mechanisms, they can affect different parts of the body. Nail involvement is important in PsO. However, nail findings in RA and AS have not been extensively investigated despite their inflammatory presentation, similar to PsO. This study aimed to investigate clinical and onychoscopic nail findings in patients with RA and AS and compare their distribution and patterns with those observed in patients with PsO and PsA. One hundred patients (25 in each group) with confirmed diagnoses of PsO, PsA, AS, and RA and at least 1 clinically detectable nail finding were included. A total of 1000 fingernails were examined clinically, and 200 fingernails were examined onychoscopically. The distributions of clinical and onychoscopic findings were assessed and compared across the 4 disease groups. Demographic data, laboratory findings (C-reactive protein, human leukocyte antigen B27, rheumatoid factor, anti-cyclic citrullinated peptide), PsO Area and Severity Index, and Nail PsO Severity Index were recorded. Pitting and onycholysis were the most common findings in PsO and PsA, leukonychia predominated in AS, and vertical ridges/trachyonychia were frequent in RA. Onychoscopy showed that clustered dotted vessels were significantly more frequent in PsO and PsA, whereas parallel dotted/short linear vessels (“fish school-like pattern”) were significantly more frequent in RA. Megacapillaries, microhemorrhagic dots, and coiled and tortuous capillaries were numerically more frequent in AS. Some vascular findings were associated with elevated C-reactive protein, human leukocyte antigen B27 positivity, and rheumatoid factor positivity. Nail findings in patients with IMIDs may reflect underlying inflammatory and vascular changes. Richer nail findings in PsO and PsA may be linked to keratinocyte-driven inflammation, whereas vascular alterations may play a more prominent role in the nail findings observed in RA and AS. Differences in clinical and onychoscopic nail patterns across disease groups suggest that detailed nail examination and onychoscopy may provide supportive clinical clues and aid in the clinical differentiation of IMIDs.

1. Introduction

Immune-mediated inflammatory diseases (IMIDs) are a group of chronic inflammatory diseases characterized by immune-mediated mechanisms. Patients with psoriasis (PsO), psoriatic arthritis (PsA), rheumatoid arthritis (RA), and ankylosing spondylitis (AS) belong to this group.^[1] IMIDs are characterized by an exaggerated immune response triggered by environmental factors in genetically predisposed individuals. This dysregulated immune response results in a chronic inflammatory process involving multiple pro-inflammatory cytokines, including tumor necrosis factor-alpha-α, interleukin-17, and interleukin-23.^[2] These cytokines contribute to chronic inflammation, immune cell recruitment, tissue remodeling, and progressive structural damage in affected tissues.^[2,3] Although IMIDs share common pathogenic mechanisms, disease-specific pathways also exist and may contribute to differences in clinical manifestations, tissue involvement, and treatment response.^[3]

Beyond their primary target tissues, IMIDs may also affect the nail unit through shared inflammatory pathways. The nail unit is increasingly recognized as more than a simple skin appendage and has a close anatomical and functional relationship with the distal interphalangeal (DIP) joint and adjacent entheses. In psoriatic disease, this relationship has led to the concept of the nail-enthesis complex, supporting a link between nail involvement and musculoskeletal inflammation.^[4–6] It has been proposed that inflammatory cytokines may spread between these interconnected structures, and inflammation involving the nail unit may extend to the surrounding periungual tissues.^[7,8] Together, these inflammatory processes may affect the nail matrix, nail bed, and periungual tissues, resulting in characteristic clinical and dermoscopic nail findings. Therefore, nail changes may serve as visible markers of underlying inflammatory activity and provide insights into disease-related inflammatory processes in IMIDs.

Nail involvement is particularly important in PsO. Depending on the anatomical structure involved, inflammation may lead to different nail manifestations. Nail matrix involvement is typically associated with pitting, leukonychia, and nail plate crumbling, whereas nail bed inflammation may result in onycholysis, subungual hyperkeratosis, splinter hemorrhages, and the oil drop sign.^[9] Nails are reported to be involved in 50 to 88% of PsO patients.^[10] This percentage can be higher in patients with PsA, especially those with DIP arthritis.^[11]

RA predominantly affects the peripheral joints, whereas AS primarily affects the axial joints and entheses. However, unlike PsO and PsA, nail findings in RA and AS have not been extensively investigated. Studies characterizing nail findings in RA remain limited, and, to the best of our knowledge, nail findings in AS have not been specifically investigated. Furthermore, comparative studies evaluating clinical and onychoscopic nail findings across PsO, PsA, RA, and AS are lacking. In this context, the aim of this study was to investigate clinical and onychoscopic nail findings in patients with RA and AS and to compare their distribution and patterns with those observed in patients with PsO and PsA.

2. Materials and methods

This prospective study was approved by the Bezmialem Vakif University Ethics Committee (Decision number: 19/366, Date: November 17, 2020) and registered at ClinicalTrials.gov (ID: NCT04709354). Informed consent was obtained from all the patients. The study was conducted between November 2020 and November 2021 and included 25 patients with PsO, 25 with PsA, 25 with RA, and 25 with AS who visited the Bezmialem Vakif University Dermatology and Rheumatology outpatient clinics during this period.

Patients diagnosed with PsO clinically and/or histopathologically and those diagnosed with PsA, RA, and AS according to the Classification Criteria for PsA, 2010 American College of Rheumatology/European League against Rheumatism, and Assessment of Spondyloarthritis International Society criteria were included in the study. Patients to be included in all groups were selected such that each had at least 1 nail finding. This selection criterion was applied to enrich the study population for nail abnormalities and enable comparative characterization of clinical and onychoscopic findings across the 4 disease groups. Patients with confirmed coexisting onychomycosis and those using biological agents for treatment were excluded because biological agents have the most significant effect on nail lesions. This approach also aimed to minimize the differences between the groups in terms of treatment.

All fingernails of the patients were examined, and dermoscopic (onychoscopic) examinations were performed on the 2 nails that were most severely affected by each patient. A total of 1000 nails were examined, and 200 nails were examined dermoscopically. Dermoscopic images were recorded using a Fotofinder Dermoscope II (FotoFinder Systems GmbH), and gel was used to clarify the image.

Demographic characteristics such as age, sex, height, and weight of all patients, as well as the presence of a family history of PsO and joint involvement, were recorded. Blood tests, including human leukocyte antigen B27, C-reactive protein (CRP), rheumatoid factor, and anti-cyclic citrullinated peptide tests, were performed. Disease severity was compared by calculating the PsO Area and Severity Index (PASI), and nail disease severity was compared by calculating the Nail PsO Severity Index (NAPSI) in PsO patients.

Before our study, a pilot analysis was conducted, and the sample was determined accordingly. According to the post hoc power analysis conducted based on the findings obtained from the study results, the difference between the rates was determined to be 0.72 for an effect size of 0.66 for n1 = n2 = n3 = n4 = 25, and the power of the study was 90% with n = 100 people.

2.1. Statistical analysis

Data distribution was analyzed using the Shapiro–Wilk test. Comparisons between 2 independent groups with a normal distribution were made using the independent sample t-test, and comparisons between 2 independent groups without a normal distribution were made using the Mann–Whitney U test. The analysis of variance test was used for comparisons involving 3 or more groups with a normal distribution, while the Kruskal–Wallis test was used for comparisons involving 3 or more groups without a normal distribution. Dunn and Bonferroni tests were used as post hoc tests for significant variables. Pearson chi-square and Fisher exact tests were used to evaluate differences between categorical variables. Descriptive statistics are expressed as mean ± standard deviation, median (min–max), and n (%) for categorical data. All statistical analyses were performed using IBM SPSS Statistics for Windows, Version 26.0 (IBM Corp., Armonk), with a significance level set at α = 0.05, and a confidence level of 95%.

3. Results

In total, 100 patients were included in this study. The mean age was 43.59 ± 12.69. There was a statistically significant difference in the mean age (P = .001), and AS patients were significantly younger (AS: 35.96 ± 9.04, RA: 50.04 ± 9.57, PsO: 44.40 ± 16.84, PsA: 43.96 ± 10.03). The study group comprised 65 female subjects and 35 male subjects. The majority of patients with joint involvement were women, and the sex distribution was statistically significant (PsA: n = 17, 68%; RA: n = 22, 88%; AS: n = 15, 60%). The demographic and clinical characteristics of patients are presented in Table 1.

Table 1.

Demographic data.

Demographic Data	PsO without joint involvement (n = 25)	PsA	AS	RA	P value
	n = 25	n = 25	n = 25	n = 25
Age, mean ± SD	44.40 ± 16.84	43.96 ± 10.03	35.96 ± 9.04	50.04 ± 9.57	.001
Gender, n (%)					.012
- Female	11 (44)	17 (68)	15 (60)	22 (88)
- Male	14 (56)	8 (32)	10 (40)	3 (12)
Weight (kg), mean ± SD	81.4 ± 15.52	80.92 ± 16.23	69.96 ± 20.23	77.32 ± 17.64	.077
Height (m), mean ± SD	1.71 ± 0.07	1.65 ± 0.07	1.67 ± 0.09	1.63 ± 0.07	.02
BMI (kg/m2), mean ± SD	25.78 ± 8.70	29.53 ± 5.57	24.90 ± 6.44	28.97 ± 6.94	.076
Family History of Psoriasis, n (%)	8 (32)	7 (28)	3 (12)	3 (12)	.172
Laboratory Data, n (%)
- Elevated CRP	2 (8.3)	8 (32)	6 (24)	16 (64)	< .001
- HLA B27 Positive	1 (14.3) (n = 7)	1 (5) (n = 20)	11 (44)	1 (5.9) (n = 17)	.007
- RF Positive	0 (n = 4)	1 (5.9) (n = 17)	0 (n = 16)	16 (64)	< .001
- Anti-CCP Positive	0 (n = 4)	0 (n = 13)	0 (n = 7)	13 (56.5) (n = 23)	< .001
PASI, mean ± SD	2.42 ± 2.94/ 1.60 (0.1–11.5)	1.51 ± 1.57/ 1.10 (0–6.5)	-	-	.382
NAPSI, mean ± SD	20.48 ± 13.12/ 19 (2–49)	20.04 ± 15.78/ 18 (2–74)	-	-	.734
Arthritis Type in PsA Patients, n (%)	-		-	-
Polyarticular	-	3 (12)	-	-
Mono-oligoarticular	-	8 (32)	-	-
DIP	-	1 (4)	-	-
Arthritis Mutilans	-	0	-	-
Spondyloarthritis	-	13 (52)	-	-

Numerical data are expressed as mean ± SD or median (range). Categorical data are expressed as frequencies (percentages).

anti-CCP = anti-citrullinated protein, AS = ankylosing spondylitis, BMI = body mass index, CRP = C-reactive protein, DIP = distal interphalangeal predominant, n = number of patients, NAPSI = Nail PsO Severity Index, PASI = PsO Area and Severity Index, PsA = psoriatic arthritis, PsO = psoriasis, RA = rheumatoid arthritis, RF = rheumatoid factor, SD = standard deviation.

3.1. Nail findings

The most common nail findings in PsO patients were pitting (88%, n = 22) and onycholysis (88%, n = 22), which were also observed at similar rates in PsA patients (onycholysis, 88%; n = 22; pitting, 80%; n = 20) (Fig. 1). The most frequently observed nail finding in the AS group was leukonychia (56%, n = 14), while vertical ridges/trachyonychia (48%, n = 12) and leukonychia (44%, n = 11) were the most frequently detected findings in the RA group (Fig. 2). The rates of visible nail findings are summarized in Table 2.

Figure 1.

Visible nail findings in PsO patients. (A) Pitting; (B) subungual hyperkeratosis (black arrow), oil drop sign (red arrow); (C) crumbling; (D) onycholysis and erythematous border of onycholysis. PsO = psoriasis.

Figure 2.

Visible nail findings in RA and AS patients. (A) Vertical ridges in RA patient; (B) leukonychia in RA patient; (C) vertical ridges in AS patient (black arrow), pitting in AS patient (black circle), (D) leukonychia in AS patient. AS = ankylosing spondylitis, RA = rheumatoid arthritis.

Table 2.

Visible nail findings.

Visible nail findings	PsO without joint involvement	PsA	AS	RA	Between PsO and PsA patients	Between AS vs RA patients P value	Between 4 groups
					P value		P value
Pitting, n (%)	22 (88)	20 (80)	6 (24)	4 (16)	.70	.72	< .001
Onycholysis, n (%)	22 (88)	22 (88)	3 (12)	9 (36)	1.0	.09	< .001
Oil drop sign, n (%)	15 (60)	12 (48)	0	0	.39	-	< .001
Horizontal ridges, n (%)	6 (24)	9 (36)	3 (12)	2 (8)	.35	1.0	.05
Splinter hemorrhage, n (%)	17 (68)	18 (72)	7 (28)	4 (16)	.75	.49	< .001
Leukonychia, n (%)	14 (56)	16 (64)	14 (56)	11 (44)	.56	.57	.56
Nail plate crumbling, n (%)	4 (16)	3 (12)	0	0	1.0	-	.03
Subungual hyperkeratosis, n (%)	10 (40)	17 (68)	4 (16)	3 (12)	.04	1.0	< .001
Red lunula, n (%)	8 (32)	8 (32)	1 (4)	2 (8)	1.0	1.0	.01
Vertical ridges-trachyonychia, n (%)	12 (48)	11 (44)	6 (24)	12 (48)	.77	.14	.25

Numerical data are expressed as the mean ± SD or median (range). Categorical data are expressed as the frequency (percentage).

AS = ankylosing spondylitis, n = number of patients, PsA = psoriatic arthritis, PsO = psoriasis, RA = rheumatoid arthritis, SD = standard deviation.

When comparing the visible nail findings among the 4 groups, pitting (P < .001), onycholysis (P < .001), oil drop (P < .001), splinter hemorrhage (P < .001), nail plate crumbling (P = .03), subungual hyperkeratosis (P < .001), and red lunula (P = .01) were significantly more common in patients with PsO. There was no significant difference between the groups in terms of leukonychia, horizontal ridges, and vertical ridges (P = .56, P = .05, and P = .25, respectively).

When pairwise comparisons were made for the variables that were significant in the 4-group comparisons, there was no difference between PsO and PsA and between RA and AS for pitting, onycholysis, oil drop, and splinter hemorrhage; however, a difference was detected between PsO and RA, PsO and AS, PsA and RA, and PsA and AS. When we examined subungual hyperkeratosis, we found that PsO differed from PsA, RA, and AS, while PsA differed only from AS and RA. There were no significant differences between the RA and AS groups.

The mean PASI was 2.42 ± 2.94 (range: 0.1–11.5) in psoriatic patients without joint involvement (PsO) and 1.51 ± 1.57 (range: 0–6.5) in PsA patients. The mean NAPSI score was 20.48 ± 13.12 (range: 2–49) in the group without joint involvement and 20.04 ± 15.78 (range: 2–74) in the PsA group. There was no significant difference in the mean PASI and NAPSI scores between the 2 groups (P = .382 and P = .734, respectively). The relationships between PASI, NAPSI, and nail findings in patients with PsO were also evaluated. There was no correlation between the PASI score and nail findings.

The types of joint involvement in patients with PsA were also examined. There was no arthritis of the mutilans type, which is the most severe type, among our patients. The most common joint involvement in PsA patients was spondylopathy, with a rate of 52% (n = 13), and mono-oligoarticular involvement, with a rate of 32% (n = 8). When examining whether there was a difference in nail findings according to the type of joint involvement, no statistically significant difference was detected.

3.2. Onychoscopic nail findings

Vascularization of the proximal nail fold was evaluated using onychoscopy. Multirow capillaries were more common than single-row capillaries in all patients. Megacapillaries (32%, n = 8), microhemorrhagic dots (32%, n = 8), and coiled and tortuous capillaries (48%, n = 12) were numerically more frequent in patients with AS (Fig. 3). Distorted, branched, and purple vessels were also numerically more frequent in patients with RA (20%, n = 5); however, the difference between the groups was not statistically significant (P = .92) (Fig. 4A). Patients with PsO (PsO: 76%, n = 19; PsA: 84%, n = 21) had more clustered dotted vessels (P < .001), whereas patients with RA (64%, n = 16) had more parallel dotted/short linear vessels (“fish school-like pattern”) (P = .01) (Figs. 4B and 4C).

Figure 3.

Vascularization of the proximal nail fold. (A) Single-row capillaries in RA patient; (B) multirow capillaries in AS patient; (C) microhemorrhagic dots in AS patient; (D) megacapillary (red arrow), coiled and tortuous capillaries (white arrow) and multirow capillaries in AS patient (black arrow). AS = ankylosing spondylitis, RA = rheumatoid arthritis.

Figure 4.

Different types of vascularization of the proximal nail fold. (A) Distorted, branched, purple vessels in RA patient; (B) clustered dotted vessels in psoriasis patient; (C) parallel dotted/short linear vessels (“fish school-like pattern”) in RA patient. RA = rheumatoid arthritis.

Multirow capillaries (53.1%, n = 17) and vascular prominence under the nail plate (62.5%, n = 20) were commonly observed in patients with high CRP levels. Multirow capillaries were also more frequently observed in the human leukocyte antigen B27 positive group (85.7%, n = 12). Multirow capillaries (52.9%, n = 9) and parallel dotted/short linear vessels (“fish school-like pattern”) were also more common in the rheumatoid factor-positive group (58.8%, n = 10).

Of the other onychoscopic nail findings, onycholysis was most common in the PsO and PsA groups (96% and 84%, respectively), vascular prominence under the nail plate was observed in the AS group (72%), and leukonychia was most common in the RA group (44%). The erythematous border of onycholysis, which is an important sign for the differential diagnosis of PsO, can be easily visualized with dermoscopy. In our study, the erythematous border of onycholysis was found in 60% of PsO patients and 64% of PsA patients, which was significantly more common (P < .001). The rates of onychoscopic nail findings are summarized in Table 3 and examples of these findings can also be seen in Figure 5.

Table 3.

Onychoscopic nail findings.

Dermoscopic nail findings	PsO	PsA	AS	RA	Between PsO and PsA patients P value	Between AS ve RA patients P value	Between 4 groups P value
Single-row capillary, n (%)	7 (28)	5 (20)	6 (24)	8 (32)	.50	.75	.79
Multirow capillaries, n (%)	16 (64)	18 (72)	17 (68)	15 (60)	.54	.76	.82
Microhemorrhagic dots, n (%)	3 (12)	6 (24)	8 (32)	4 (16)	.46	.32	.31
Megacapillary, n (%)	5 (20)	6 (24)	8 (32)	7 (28)	.73	1.0	.79
İrregular, coiled and tortuous capillaries; n (%)	10 (40)	9 (36)	12 (48)	10 (40)	.77	.77	.85
İrregular,distorted, branched, purple vessels; n (%)	4 (16)	3 (12)	3 (12)	5 (20)	1.0	.70	.92
Clustered dotted vessels; n (%)	19 (76)	21 (84)	6 (24)	6 (24)	.48	1.0	< .001
Parallel dotted/short linear vessels (“fish school-like pattern”); n (%)	6 (24)	6 (24)	10 (40)	16 (64)	1.0	.15	.01
Splinter hemorrhage, n (%)	18 (72)	20 (80)	6 (24)	5 (20)	.50	1.0	< .001
Pitting, n (%)	18 (72)	20 (80)	5 (20)	3 (12)	.50	.70	< .001
Horizontal ridges, n (%)	5 (20)	8 (32)	2 (8)	1 (4)	.33	1.0	.04
Red lunula, n (%)	12 (48)	8 (32)	2 (8)	3 (12)	.24	1.0	.003
Onycholysis, n (%)	21 (84)	24 (96)	6 (24)	10 (40)	.34	.36	< .001
Erythematous border of onycholysis, n (%)	15 (60)	16 (64)	1 (4)	2 (8)	.77	1.0	< .001
Oil drop sign, n (%)	15 (60)	13 (52)	0	0	.56	-	< .001
Subungual hyperkeratosis, n (%)	12 (48)	18 (72)	8 (32)	6 (24)	.08	.75	.003
Leukonychia, n (%)	16 (64)	18 (72)	14 (56)	11 (44)	.54	.57	.21
Dilated capillary in hyponychium, n (%)	18 (72)	13 (52)	16 (64)	11 (44)	.14	.25	.19
Vascular prominence under the nail plate, n (%)	16 (64)	19 (76)	18 (72)	18 (72)	.35	1.0	.82

Numerical data are expressed as the mean ± SD or median (range). Categorical data are expressed as the frequency (percentage).

AS = ankylosing spondylitis, n = number of patients, PsA = psoriatic arthritis, PsO = psoriasis, RA = rheumatoid arthritis, SD = standard deviation.

Figure 5.

Other dermoscopic findings of nail. (A) Splinter hemorrhage (black arrow) and oil drop sign (red arrow); (B) pitting; (C) horizontal ridges; (D) red lunula; (E) onycholysis and erythematous border of onycholysis (black arrow), splinter hemorrhage (red arrow); (F) oil drop sign; (G) subungual hyperkeratosis (black arrow), dilated capillary in hyponychium (black circle); (H) leukonychia; (I) dilated capillary in hyponychium; (J) vascular prominence under the nail (red arrow), leukonychia (black arrow).

When pairwise comparisons were made for the variables that were significant in the 4-group comparisons, there was no difference between PsO and PsA and between RA and AS for clustered dotted vessels and the erythematous border of onycholysis; a difference was detected between PsO and RA, PsO and AS, PsA and RA, and PsA and AS. When we looked at parallel dotted/short linear vessels (“fish school-like pattern”), we found that RA differed from PsO, PsA, and AS, while there was no difference between PsO and PsA. In the comparison of red lunula, we found that PsA differed from PsO, RA, and AS, while there was no difference between RA and AS.

4. Discussion

The high prevalence of nail involvement in PsA raises questions about the relationship between the nails and joints in other IMID diseases. PsO can cause enthesitis with or without inflammatory arthritis. Enthesitis is not simply a local inflammation but an inflammation of the enthesis organ, which consists of bones, tendons, and ligaments. The ligaments of the extensor tendon are not directly attached to the bone but expand and surround the nail. These findings support the anatomical and functional relationship between the nail unit and the DIP joint.^[5] Studies have shown a significant association between psoriatic nail involvement and DIP arthritis, suggesting the spread of active inflammatory cells owing to anatomical proximity.^[11] In addition, nail anomalies have been reported in nearly every patient with enthesitis detected using ultrasonography.^[12] It has been proposed that inflammatory cytokines may spread between the nail unit and adjacent musculoskeletal structures, while inflammation involving the nail unit may also extend to surrounding periungual tissues.^[7,8] These mechanisms may contribute to the development of characteristic nail findings in inflammatory diseases. However, unlike PsO and PsA, nail involvement in RA and AS has not been extensively investigated despite their inflammatory nature. In our study, we identified prominent nail findings in patients with PsO, consistent with previous reports. We observed that vertical ridges were common in patients with RA, whereas leukonychia was frequently observed in AS patients. Onychoscopic examination revealed distinct and diverse findings across the disease groups. The spectrum of onychoscopic findings observed in our study may reflect underlying inflammatory and vascular processes affecting the nail unit. Despite shared immune-mediated inflammatory mechanisms and anatomical relationships between the nail unit and adjacent musculoskeletal structures, richer nail findings in psoriatic disease may be related to the central role of keratinocytes in its pathogenesis. To the best of our knowledge, no studies have included nail findings in AS, and there are a limited number of studies on nail changes in RA.

In our study, the most common nail findings in patients with PsO, with or without joint involvement, were pitting and onycholysis (PsO, n = 22, 88%; PsA, n = 20, 80%), consistent with the findings of previous studies.^[10,13–16] Leukonychia was the most common finding in the AS group (56%, n = 14). It is believed that leukonychia may develop as a result of keratinization disorders in the nail matrix due to inflammation. Pitting and leukonychia, which are both thought to result from keratinocyte abnormalities due to inflammation, were also observed in patients with RA and AS. However, since keratinocyte abnormalities are likely more pronounced in PsO due to the vicious inflammatory cycle involving both keratinocytes and T cells, this mechanism may contribute to the richer nail findings observed in patients with psoriatic disease in our study.

In the RA group, vertical ridges, also known as trachyonychia, were the most common finding (48%, n = 12). In a study conducted by Michel C, vertical ridges were more common in patients with RA, and it was emphasized that this situation was more numerous and severe than vertical ridges that increased with age.^[17] It is thought that vertical ridges may be the result of microvascular disease in the nail bed, but the cause of vertical ridges and their frequent beaded appearance is still unknown.^[18] Similarly, although leukocytoclastic vasculitis is more frequently observed in association with RA, its occurrence in AS is relatively rare.^[19] This may reflect vascular complications that more commonly accompany RA. In our study, the occurrence of vertical ridges across all 4 disease groups may support a potential relationship with microvascular changes. However, although several microvascular changes were observed in patients with AS, vertical ridges were less common, suggesting that additional factors may also be involved in their pathogenesis. There were no significant differences between the groups in terms of leukonychia, horizontal ridges, and vertical ridges. Oil drop signs and nail plate crumbling were not observed in the patients with AS and RA. These 2 nail findings were mentioned as being specific to PsO and have not been investigated in RA and AS patients until now.

Dermoscopy is a noninvasive tool that has recently been used to evaluate the features of inflammatory skin diseases and nail bed vascularity anomalies in rheumatological diseases.^[20] Systemic inflammatory diseases involve the activation of the vascular endothelium, as evidenced by the detection of intercellular adhesion molecule 1 and vascular cell adhesion molecule 1 in the skin and synovial membrane of PsO and PsA patients.^[21] Nail fold vascular alterations have been attributed to dysregulated angiogenesis and inflammation-related capillary damage, reflecting the underlying inflammatory processes in PsO and PsA. Similar mechanisms have also been described in RA, although vascular changes appear to be less pronounced.^[22] In our study, nail bed vascular anomalies were detected in all the IMID group diseases, as expected. Multirow capillaries were more commonly observed in the proximal nail fold in all groups, possibly reflecting chronic inflammatory processes. Increased vascularity under the nail plate and multirow capillaries were associated with higher CRP levels (53.1%, n = 17), suggesting a relationship between vascular changes and inflammation in the nail bed.

Megacapillary (32%, n = 8), microhemorrhagic dots (32%, n = 8), and coiled and tortuous vessels (48%, n = 12) were numerically more frequent in patients with AS. Distorted, branched, and purple vessels were also numerically more frequent in patients with RA (20%, n = 5); however, the difference between the groups was not statistically significant. Sinem Sag et al reported that purplish vessels, overlapping and twisted vessels, avascular areas, and microhemorrhagic dots were found more frequently in patients with RA than in the control group.^[23] Graceffa et al compared patients with PsO, PsA, RA, and the control group and found a significant difference in periungual vascularity in all groups compared to the control group. According to this study, overlapping and twisted vessels are more detectable in PsO than in RA.^[21]

Nail dermoscopy (onychoscopy) has been suggested as a useful tool for differentiating PsA from RA. Sparsely clustered or diffuse dotted vessels are more common in patients with PsA, while parallel dotted/short linear vessels (“fish school-like pattern”) and distorted, branched, and purple vessels are more common in patients with RA.^[20,24] Similarly, in our study, clustered dotted vessels were more common in patients with PsO (76% in the group without joint involvement, n = 19; 84% in the group with PsA, n = 21) (P < .001), and parallel dotted/short linear vessels (“fish school-like pattern”) were significantly more common in RA patients, with a rate of 64% (n = 16) (P = .01). These differences were also supported by post hoc pairwise comparisons of clustered dotted vessels and parallel dotted/short linear vessels. In fact, the clustered dots observed in the nail bed in PsO can also be seen in skin lesions, and they may even present as the Auspitz sign.^[25] Distorted, branched, and purple vessels were also numerically more frequent in patients with RA, although the difference between the groups was not statistically significant (n = 5, 20%; P = .92). Taken together, the vascular manifestations, trachyonychia, and onychoscopic findings observed in patients with RA may reflect vascular alterations accompanying the underlying inflammatory process.

To our knowledge, our study is the first to compare the clinical and onychoscopic nail findings among the 4 groups. Our study has some limitations. First, only patients with at least 1 clinically detectable nail finding were included. Therefore, our findings may not be generalizable to unselected patient populations, and the true frequency of nail involvement in each disease cannot be estimated. Second, our study did not include a healthy control group. Although the primary aim of our study was to compare nail findings across 4 inflammatory disease groups, the absence of a healthy control group limits the assessment of the disease specificity of the observed findings. In addition, the sample size of the study was relatively small, but we attempted to overcome this problem with a prior power analysis.

5. Conclusion

In conclusion, nail findings in patients with IMIDs may reflect underlying inflammatory and vascular changes. Richer nail findings in patients with PsO and PsA may be related to the central role of keratinocytes in psoriatic disease. Pitting, onycholysis, splinter hemorrhage, and subungual hyperkeratosis were more common in patients with PsO, whereas leukonychia, horizontal ridges, and vertical ridges did not differ significantly between the disease groups. Clustered dotted vessels were more common in patients with PsO and PsA, whereas parallel dotted/short linear vessels (“fish school-like pattern”) were more common in patients with RA. These differences in clinical and onychoscopic nail patterns suggest that detailed nail examination and onychoscopy may provide supportive clinical clues and aid in the clinical differentiation of IMIDs. More detailed studies on nail findings in IMIDs would be beneficial for further understanding their potential clinical significance and the pathogenesis of nail disorders other than PsO.

Author contributions

Conceptualization: Begüm Güneş, Ozan Volkan Yurdakul, Nazan Yilmaz, Nahide Onsun.

Data curation: Begüm Güneş, Ozan Volkan Yurdakul, Özlem Su Küçük, Nahide Onsun.

Formal analysis: Ayşegül Yabaci Tak.

Investigation: Begüm Güneş, Nahide Onsun.

Methodology: Begüm Güneş, Ayşegül Yabaci Tak.

Project administration: Özlem Su Küçük, Nahide Onsun.

Resources: Begüm Güneş, Nazan Yilmaz.

Supervision: Ozan Volkan Yurdakul, Nazan Yilmaz, Nahide Onsun.

Writing – original draft: Begüm Güneş.

Writing – review & editing: Begüm Güneş, Ozan Volkan Yurdakul, Nahide Onsun.