Musculoskeletal and nail ultrasound findings in children with psoriasis: a case-control study

Abstract

Background

Children with psoriasis can develop juvenile psoriatic arthritis. Musculoskeletal ultrasound is a helpful imaging modality in the early recognition of joint inflammation. This pilot study aims to describe clinical and subclinical joint and nail abnormalities in children with psoriasis.

Methods

Children with psoriasis and healthy controls underwent ultrasound examination of various joints, entheses, and nails. Using a standard acquisition protocol, images were obtained in both B-mode and PD-mode. Differences between psoriasis and control groups were examined.

Results

Fifteen psoriasis patients who were not on systemic therapy and did not have clinical signs of arthritis and thirteen age- and sex-matched healthy controls were enrolled. While patients with psoriasis demonstrated subclinical synovitis in the finger, knee, and ankle joints more frequently than the control group (p = 0.047), no statistically significant difference was observed in the comparison of each specific joint. PD positivity was detected at the entheses in two patients with psoriasis and at three entheseal sites of two healthy children. Nail ultrasound examination demonstrated significantly thicker nail beds (1.6 vs. 1.4 mm, p < 0.001) and more frequent abnormal nail structure (70% vs. 21.2%, p < 0.001) in the psoriasis group compared to control group while the thickness of the nail plate and nail matrix were similar. Type II nail morphology changes were the most frequently detected type according to the Wortsman classification. Positive PD-mode findings in the nail bed and nail matrix were more common in the control group (both p < 0.001). Among the psoriasis cohort, nails with abnormal exam findings had significantly thicker nail plate (0.4 vs. 0.35 mm, p = 0.003) and nail bed (1.8 vs. 1.6 mm, p = 0.006) measurements compared to nails with normal examination.

Conclusions

Ultrasound is a useful tool for evaluating inflammatory joint and nail findings that may help delineate subclinical joint inflammation in children with psoriasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12969-026-01209-4.

Background

Psoriasis is a chronic inflammatory immune-mediated skin disease affecting 2.5-3% of the general population, with nearly one-third of cases beginning in childhood [1]. Approximately 1 to 10% of children with psoriasis develop juvenile psoriatic arthritis (JPsA), a destructive arthropathy that can lead to permanent joint damage, physical impairment, chronic pain, and functional limitation [2, 3]. JPsA is considered a subtype of juvenile idiopathic arthritis (JIA), defined by the International League of Associations for Rheumatology (ILAR) with an onset of persistent arthritis prior to age 16 with either presence of skin psoriasis, or in the absence of rash, presence of at least two of the following: nail changes (nail pitting or onycholysis), dactylitis, and psoriasis in a first-degree relative [4]. In addition to arthritis and dactylitis, enthesitis and axial skeleton involvement are among the musculoskeletal manifestations of JPsA [5]. Since the temporal relationship between the onset of psoriasis and arthritis varies, early recognition of musculoskeletal involvement in psoriasis is crucial as delay in diagnosis and therapeutic intervention in JPsA is associated with worse long-term outcomes and disability [1].

The use of musculoskeletal ultrasonography (MSUS) has emerged over the last several years as an objective and sensitive imaging modality for the evaluation of joint inflammation in JIA [6]. Several studies have shown that MSUS is more sensitive than physical examination in the detection of subclinical synovitis, which has been reported in nearly 30% of children with JIA [7]. MSUS is also a successful imaging technique in detecting early and late findings of psoriatic arthritis (PsA) in adults [8, 9]. Previous studies utilizing B-mode and Power Doppler (PD)-mode MSUS imaging have demonstrated subclinical synovitis, tendon pathology, and entheseal changes in patients with PsA without any symptoms or signs of arthritis [10, 11]. Loss of the nail plate trilaminar structure, involvement of the extensor tendon at the level of the distal interphalangeal (DIP) joint, and increased vascularization have been described with variable prevalence on ultrasound assessment of the nail unit structures in patients with psoriasis and PsA [12]. Longitudinal studies have shown that subclinical findings on MSUS and nail ultrasound findings may serve as a clinical predictor of PsA development, as these psoriasis patients with ultrasound abnormalities are more likely to develop active PsA [11]. While there are a robust number of ultrasound studies in adult psoriasis and PsA patients, similar investigations among the pediatric psoriatic and JPsA population are scarce [13].

The aim of this study is to describe clinical and subclinical joint and nail abnormalities in children with psoriasis who have no known history of arthritis in comparison with healthy children.

Methods

Study group

Pediatric patients with psoriasis confirmed by a dermatologist and age and sex-matched healthy controls were enrolled in the study between February 2022 and May 2023. Children under 18 who could tolerate and cooperate with ultrasound examinations were included. Exclusion criteria were other autoimmune conditions, other nail disorders or chronic joint-related disorders, acute joint injury, trauma, or joint surgery within the last 3 months, systemic immunosuppressant treatment or oral corticosteroids in the last 2 months and pregnancy. The study was reviewed and approved by the Institutional Review Board of Cincinnati Children’s Hospital Medical Center (IRB#2021 − 0756), and the parents and patients gave written informed consent and assent to participate in the study.

All patients underwent a standard musculoskeletal joint examination performed by a pediatric rheumatologist using the Pediatric Rheumatology Collaborative Study Group (PRCSG) methodology employed in numerous FDA and NIH clinical trials to determine active joint count [14]. Beighton score was also recorded with a score higher than 5 indicating hypermobility [15]. To measure the severity of psoriasis and nail involvement, photographs of the skin and nails of each subject were taken using a standard protocol by a medical photographer. Psoriasis Area and Severity Index (PASI) and Nail Psoriasis Severity Index (NAPSI) scores were then computed by a single pediatric dermatologist experienced in psoriasis (CB). A PASI score of 5 to 10 was considered moderate disease, and a score over 10 was considered severe [16].

Patients reported joint pain using a Likert scale (0-no pain to 10-worst pain possible), duration of morning stiffness, and frequency of non-steroidal anti-inflammatory drug (NSAID) use over the past 2 weeks. All enrolled subjects (or parents when appropriate) also completed the short form upper extremity, physical activity, and mobility Patient-Reported Outcomes Measurement Information System (PROMIS) questionnaires, a validated instrument that evaluates physical activity level and function. Higher PROMIS scores indicate better physical function [17]. Data collection included demographics, past medical history, past and current medications for psoriasis, and body mass index (BMI). For psoriasis patients, clinical data such as psoriatic disease subtype, duration of disease, and presence of nail involvement were gleaned from their medical records when available.

MSUS and nail ultrasound examination

Each participant underwent a one-time MSUS and nail ultrasound examination using a high-resolution ultrasound machine (either the General Electric Logiq S8 XDClear or Logiq Fortis). An 8–18 MHz or 18–24 MHz small-footprint linear transducer was used for the fingers and nails depending on the ultrasound machine utilized during the examination. The following sites were scanned bilaterally: fingernail units, metacarpophalangeal (MCP), proximal interphalangeal (PIP) and DIP joints of the second and third fingers, as well as any finger with psoriatic nail involvement, knee (suprapatellar, medial and lateral parapatellar recesses) and ankle joints (tibiotalar and medial and lateral aspect of the subtalar joint). Additionally, the following entheses were examined: quadriceps insertion on the proximal pole of the patella, proximal and distal patellar tendon insertion, Achilles tendon insertion on the calcaneus, and proximal calcaneal plantar fascia insertion. Images were obtained by both B-mode and PD-mode ultrasound imaging using a standard acquisition protocol [18, 19]. Ultrasound examination was performed by or under the direct supervision of a licensed pediatric rheumatologist with specific MSUS certification by the American College of Rheumatology (PVF, TT). To evaluate the feasibility, the duration of the ultrasound examination was recorded. Participants were also asked to complete brief questionnaires about the acceptability of the ultrasound to evaluate their overall experience during the procedure.

De-identified ultrasound images were scored for the presence of synovitis by one of two reviewers (PVF, TT) according to the pediatric-specific semiquantitative scoring system (range 0 to 3) for synovitis proposed by the Childhood Arthritis and Rheumatology Research Alliance (CARRA) MSUS workgroup, which includes validated scoring protocols for the fingers, knees, and ankles [18, 19]. B-mode ultrasound findings of grade 0 or 1 were regarded as physiological and negative for synovitis. B-mode findings of grades 2 (moderate) and 3 (severe) were considered positive for synovitis. The PD-mode images were scored only if B-mode findings were regarded as positive and PD signals were within the synovial recess. For PD-mode imaging, grades 1 to 3 were categorized as positive [18]. Enthesitis was evaluated according to the Outcome Measures in Rheumatology (OMERACT) definition, assessing for tendon thickening, hypoechogenicity, bony changes, and PD activity at the entheses [20], and scored on a dichotomous scale (0-negative, 1-positive).

For nail ultrasound imaging, parameters including the thickness of the nail plate, nail bed, nail matrix, and finger distal extensor tendon were measured in longitudinal view (Supplementary Fig. 1). Specifically, nail plate thickness was defined as the maximum distance between the dorsal and ventral plates. Nail bed thickness was measured in the middle third of the phalanx as the distance between the ventral plate and edge of the phalangeal bone. The nail matrix was the isoechogenic area measured at the proximal end of the nail bed under the proximal nailfold. The thickness of the distal extensor tendon was measured at the place of attachment to the distal phalanx [21]. Nail plate structure was also evaluated utilizing the Wortsman classification, a qualitative assessment of the severity of psoriatic nail changes, with type I being least severe and type IV being most severe [21]. Morphology type was determined by consensus discussion of three reviewers (PVF, TT, LN). According to the Wortsman classification, type I was defined as focal hyperechoic involvement of the ventral plate, type II as loosening of the ventral plate borders, type III as wavy plates, and type IV as loss of definition of both plates [22]. A semi-quantitative scoring approach was utilized for PD-mode findings in the nail bed and nail matrix, with grade 0 meaning no PD signal, grade 1 as signal present on less than 25% of the examined area, grade 2 as signal present on more than 25% but less than 50% of the examined area, and grade 3 as signal present on more than 50% of the examined area [23].

Statistical analysis

Descriptive statistics were calculated using frequency (%) for categorical and mean (standard deviation (SD)) or median (interquartile range (IQR)) for continuous variables. Differences in categorical variables between the psoriasis and control groups were evaluated using Chi-square (or Fisher’s exact test when cell sizes were less than 5). Differences between continuous variables with a normal distribution were assessed using Student’s t-test, whereas continuous variables with a non-normal distribution were compared using a Wilcoxon rank sum test. In addition, Chi-square and Wilcoxon rank sum tests were used to examine the differences between normal and abnormal nail findings specific to the psoriasis group according to patients’ nail examination for ultrasound findings. SAS 9.4 was used for statistical analyses and statistical significance was accepted when p < 0.05.

Results

Patient characteristics

The demographics and clinical characteristics of the participants are summarized in Table 1. A total of 15 pediatric patients with psoriasis and 13 age- and sex-matched healthy controls were included in the study. The mean disease duration was 5.8 (4.1) years in children with psoriasis. Clinical subtypes of psoriasis included eight (53.3%) with plaque psoriasis, four (26.7%) with guttate psoriasis, and three (20%) with nail psoriasis. Six patients (40%) had scalp and two (13.3%) had palmoplantar involvement. The majority of patients had mild psoriasis with a median PASI score of 2.4 (0.3–5.8). The median NAPSI score was 0 (0-2.7), and psoriasis subjects had significantly more frequent abnormal clinical nail findings (pitting, onycholysis, subungual hyperkeratosis, oil-drop discoloration, or crumbling). Concerning treatments, 11 psoriasis patients (73.3%) were actively using topical corticosteroids, with other topical therapies and phototherapy utilized less frequently. Three children with psoriasis (20%) were not receiving any treatment at the time of the study. On musculoskeletal examination, four psoriasis patients (26.7%) endorsed arthralgia, all involving the lower extremities or back, whereas none of the healthy controls exhibited joint pain. Four patients in the psoriasis group and one child in the control group were found to have hypermobility. None of the subjects enrolled displayed any clinical findings of arthritis. There was no significant difference between patient-reported pain scores between psoriasis subjects and controls. Morning stiffness for longer than 15 min was identified in five patients with psoriasis while it was not present in the control group (p = 0.044).

Table 1.

Patient characteristics of the study population

	Psoriasis Group (n = 15)	Control Group (n = 13)	p-value
Age, years, median (IQR)	11.8 (10.6–13.2)	11.6 (10.0-13.2)	0.854
Sex, n (%)			0.275
Male  Female	8 (53.3) 7 (46.7)	6 (46.2) 7 (53.8)
Race, n (%)
White  Black  Asian  Other	11 (73.3) 3 (20.0) 1 (6.7) 0 (0)	9 (69.0) 0 (0) 3 (23.1) 1 (7.7)	0.314 0.139 0.210 0.464
Ethnicity, n (%)
Hispanic	0 (0)	3 (23.1)	0.087
BMI, kg/m2, median (IQR)	18.5 (16.0-23.7)	18.1 (17.5–20.6)	0.890
Physical examination of nails, n (%)			< 0.001
Normal  Abnormal	52 (65.0) 28 (35.0)	52 (100) 0 (0)
Physical examination of joints, n (%)			NA
Normal  Abnormal	79 (100) 0 (0)	52 (100) 0 (0)
Pain level (1–10), median (IQR)
Last week  Current	1 (0–4) 0 (0–4)	1 (0–2) 0 (0–0)	0.302 0.101
PROMIS, mean (SD)
Upper extremity T-score  Mobility T-score  Physical activity T-Score	45.1 (10.5) 51.3 (7.3) 48.2 (7.8)	53.6 (6.1) 56.8 (4.7) 54.2 (8.3)	0.014 0.026 0.059

IQR: interquartile range, BMI: body mass index, NA: not applicable, PROMIS: patient-reported outcomes measurement information system, SD: standard deviation

MSUS findings of the joints and entheses

MSUS findings of the joints and entheses between the study groups are presented in Table 2. Although patients with psoriasis demonstrated subclinical synovitis in the finger, knee, and ankle joints on MSUS (total positive joint n = 27) more frequently than the control group (total positive joint n = 9) (p = 0.047), no statistically significant difference was observed in the comparison of each specific joint. None of the joints demonstrated PD signals within the synovial recess. MSUS B-mode findings of synovitis for each specific joint are detailed in Supplementary Table 1, with images of grade 2 findings demonstrated in Fig. 1.

Table 2.

MSUS findings of the joints and entheses between the study groups

Synovitis in specific joint, n (%)*	Psoriasis Group (n = 15)		Control Group (n = 13)		p-value
	Negative	Positive	Negative	Positive
Finger
MCP  PIP  DIP	77 (96.2) 65 (82.3) 75 (93.8)	3 (3.8) 14 (17.7) 5 (6.2)	52 (100) 48 (92.3) 50 (96.0)	0 (0) 4 (7.7) 2 (4.0)	0.219 0.057 0.243
Knee	27 (90.0)	3 (10.3)	26 (100)	0 (0)	0.157
Ankle	28 (93.3)	2 (6.7)	23 (88.5)	3 (11.5)	0.592
PD activity at specific tendon insertion, n (%)**	Negative	Positive	Negative	Positive	p -value
Quadriceps	29 (96.7)	1 (3.3)	24 (92.3)	2 (7.7)	0.592
Proximal patellar	30 (100)	0 (0)	26 (100)	0 (0)	NA
Distal patellar	30 (100)	0 (0)	25 (96.1)	1 (3.9)	0.464
Achilles tendon	30 (100)	0 (0)	26 (100)	0 (0)	NA
Calcaneal plantar fascia	29 (96.7)	1 (3.3)	26 (100)	0 (0)	1.000

MSUS: musculoskeletal ultrasound, MCP: metacarpophalangeal, PIP: proximal interphalangeal, DIP: distal interphalangeal, PD: Power Doppler, NA: not applicable

*A positive joint on MSUS was defined as grade 2 or 3 synovitis on B-mode. Negative was defined as grade 0 or 1. None of the joints demonstrated grade 3 findings of synovitis

**None of the entheses showed positive B-mode findings of enthesitis

Fig. 1.

Examples of B-mode abnormalities on MSUS. A: grade 2 effusion of the volar aspect of a proximal interphalangeal joint recess. B: grade 2 effusion of the lateral aspect of a subtalar ankle joint recess

PD positivity was visualized in two psoriasis patients, one at the quadriceps enthesis and one at the calcaneal plantar fascial insertion. In the control group, two children had positive PD signals at the quadriceps insertion and one of these at the distal patellar insertion additionally (Table 2). Entheseal PD positivity was not found in patients with hypermobility. No structural abnormalities of the entheses were observed in B-mode for both psoriasis patients and healthy controls.

Nail ultrasound findings

Nail ultrasound findings were investigated in 80 nails in the psoriasis group and 52 nails in the control group (Table 3). Regarding nail measurements, nail bed thickness was significantly higher in the psoriasis group compared to controls (1.6 (1.5–1.8) vs. 1.4 (1.3–1.6) mm, p < 0.001), whereas the thickness of the nail plate and nail matrix were similar between these groups. Fifty-six nails (70%) in the psoriasis cohort had abnormal nail structure per the Wortsman classification by nail ultrasound. In the psoriasis group, type II changes were most frequently observed with 28 (35%) of nails demonstrating loosening of the ventral plate border, followed by 22 nails (27.5%) with type I changes, and more rarely type IV at 7.5% (Fig. 2). Type I and type II changes were observed in 7 (13.5%) and 4 (7.7%) nails in the control group, respectively. None of the participants exhibited type III changes. When only the psoriasis cohort was analyzed (Table 4), nails with abnormal clinical examination (n = 28) had significantly thicker nail plate (0.4 (0.4–0.5) vs. 0.35 (0.3–0.4) mm, p = 0.003) and nail bed (1.8 (1.6–1.9) vs. 1.6 (1.5–1.7) mm, p = 0.006) measurements compared to nails with normal examination (n = 52). Wortsman classification and PD-mode findings did not differ according to the clinical nail involvement in patients with psoriasis.

Table 3.

Nail ultrasound findings of the study groups

	Psoriasis Group	Control Group	p-value
Nail plate thickness, mm, median (IQR)	0.4 (0.3–0.5)	0.4 (0.3–0.4)	0.230
Nail bed thickness, mm, median (IQR)	1.6 (1.5–1.8)	1.4 (1.3–1.6)	< 0.001
Nail matrix thickness, mm, median (IQR)	1.4 (1.2–1.6)	1.5 (1.3–1.6)	0.073
Finger distal extensor tendon thickness, mm, median (IQR)	0.6 (0.4–0.8)	0.6 (0.4–0.7)	0.109
Wortsman classification, n (%)			< 0.001
Normal  Type I  Type II  Type III  Type IV	24 (30.0) 22 (27.5) 28 (35.0) 0 (0) 6 (7.5)	41 (78.8) 7 (13.5) 4 (7.7) 0 (0) 0 (0)
PD-mode findings in the nail bed, n (%)			< 0.001
Grade 0  Grade 1  Grade 2  Grade 3	43 (54.4) 26 (32.9) 7 (8.9) 3 (3.8)	12 (23.1) 34 (65.4) 5 (9.6) 1 (1.9)
PD-mode findings in the nail matrix, n (%)			< 0.001
Grade 0  Grade 1  Grade 2  Grade 3	46 (58.2) 20 (25.3) 6 (7.6) 7 (8.9)	20 (38.5) 18 (34.6) 13 (25.0) 1 (1.9)

IQR: interquartile range, PD: Power Doppler

Fig. 2.

Nail morphology visualized according to the Wortsman classification. A: normal nail. B: Type I – focal hyperechoic involvement of the ventral plate. C: Type II – loosening of the ventral plate borders. D: Type IV – loss of definition of both plates. Type III changes (wavy plates) were not seen in any patients

Table 4.

Nail ultrasound findings of the psoriasis group according to clinical nail examination

	Abnormal Nail Examination* (n = 28)	Normal Nail Examination (n = 52)	p-value
Nail plate thickness, mm, median (IQR)	0.4 (0.4–0.5)	0.35 (0.3–0.4)	0.003
Nail bed thickness, mm, median (IQR)	1.8 (1.6–1.9)	1.6 (1.5–1.7)	0.006
Nail matrix thickness, mm, median (IQR)	1.3 (1.1–1.5)	1.4 (1.25–1.6)	0.174
Finger distal extensor tendon thickness, mm, median (IQR)	0.6 (0.45–0.75)	0.7 (0.45–0.8)	0.323
Wortsman classification, n (%)			0.095
Normal  Type I  Type II  Type III  Type IV	8 (28.6) 7 (25.0) 8 (28.6) 0 (0) 5 (17.9)	16 (30.8) 15 (28.8) 20 (38.5) 0 (0) 1 (1.9)
PD-mode findings in the nail bed, n (%)			0.851
Grade 0  Grade 1  Grade 2  Grade 3	14 (50.0) 11 (39.8) 2 (7.1) 1 (3.6)	29 (56.8) 15 (29.4) 5 (9.8) 2 (3.9)
PD-mode findings in the nail matrix, n (%)			0.662
Grade 0  Grade 1  Grade 2  Grade 3	16 (57.1) 9 (32.1) 1 (3.6) 2 (7.1)	30 (58.8) 11 (21.6) 5 (9.8) 5 (9.8)

IQR: interquartile range, PD: Power Doppler

*Abnormal nail examination defined by presence of pitting, onycholysis, subungual hyperkeratosis, oil-drop discoloration, or crumbling.

Feasibility of ultrasound examination

The mean duration to complete the ultrasound examination was 56.9 (20.2) minutes and all participants tolerated the entire duration of the procedure. Overall, participants found the examination protocol acceptable without pain or discomfort and felt that other children could tolerate having the ultrasound performed in the clinic setting.

Discussion

This pilot study is one of the earliest reports in the literature to present joint and nail ultrasound findings in children with psoriasis. The study demonstrates subclinical synovitis detected by MSUS in a considerable number of pediatric psoriasis patients without clinical signs of joint inflammation and off systemic treatment when compared to healthy children (9% vs. 4% of the scanned joints, respectively), however there was no significant difference observed in the comparison of individual joint locations. The latter finding may be due to the small sample size of this investigation or could reflect a more diffuse polyarticular pattern of subclinical inflammation in children with psoriasis, underscoring the value of a comprehensive multi-joint sonographic assessment. Additionally, psoriasis patients had an abnormal nail structure on ultrasound more frequently (70% vs. 21%) and most commonly demonstrated type II morphology of the nail plate. These results support the need to further define the role of ultrasound in children with skin psoriasis for the detection of subclinical joint inflammation and to define inflammatory nail findings.

A recent study in pediatric psoriasis found that patients experiencing musculoskeletal pain exhibited a significantly higher prevalence of synovitis and enthesitis on MSUS compared to those without symptoms. Notably, systemic treatment was significantly more common among asymptomatic patients. Furthermore, 20% of symptomatic patients with psoriasis were subsequently diagnosed with JPsA [13]. In our study, we enrolled children with psoriasis who were not on systemic therapy. We observed that children with psoriasis had relatively lower PROMIS scores of upper extremity, mobility, and physical activity when compared to healthy children, suggesting a tendency for worse outcome measures of functionality in this patient population. Although no clinical findings of arthritis were detected, patients with psoriasis complained of morning stiffness more frequently, and 27 of the scanned joints (9%) showed positive MSUS findings of synovitis, evidenced by grade 2 B-mode findings. These results may support the relationship between the inflammatory skin disease of psoriasis and subclinical joint inflammation. On the other hand, PD positivity at the entheses was detected in two patients with psoriasis and three entheseal sites of two children in the control group. It has been similarly shown that PD signals are mostly present at lower extremity entheses in healthy children, particularly at the quadriceps and distal patellar entheses, while B-mode assessments are normal [24]. These findings suggest that PD positivity at the entheses may not necessarily indicate an abnormality and could be physiological in children. Therefore, the acknowledgment of the clinical context of these subclinical findings detected by ultrasound is mandatory. Additional larger and longitudinal studies are needed to determine the role of MSUS in detecting and treating joint inflammation earlier.

Nail ultrasound was also a focus of the current study as the concept of the nail unit as a musculoskeletal appendage has gained an increasing amount of attention over recent years by both dermatologists and rheumatologists [25]. It is well-established that nail involvement is a predictor for the development of PsA, and the nail-enthesis complex may serve as a link between skin and joint disease [25]. Our study demonstrated more frequent abnormal nail structure by MSUS among psoriasis patients compared to controls, with a notable predominance of type II changes. This finding differs from nail ultrasound studies performed in adult patients with skin psoriasis only, where type I changes were most commonly seen. Notably, studies in adult PsA patients demonstrated that nail plate morphology primarily exhibited Type II changes on Wortsman classification [22, 25, 26]. Children with psoriasis may thus exhibit a more pathologic nail plate phenotype on MSUS than adults with skin psoriasis alone. Nail ultrasound findings specifically in healthy children have not been described in the literature before. Further, mild nail sonographic changes may not be specifically attributed to psoriasis; other factors which were not accounted for may be contributing to abnormal nail plate structures such as nail biting and microtrauma.

Previous ultrasound studies in the adult psoriatic population have demonstrated significantly increased thickness of the nail plate, nail bed, and nail matrix compared to controls which was markedly thicker in psoriatic patients even without any clinical nail findings [22, 26]. In our study, psoriasis patients had a significantly thicker nail bed when compared to healthy children. PD signal presence in the nail bed and matrix is another measure that has been utilized in the assessment of inflammatory activity of the nail apparatus in psoriatic and PsA patients, as increased vascularization is implicated in the pathogenesis of these diseases [21]. However, in the current study, PD-mode findings in the nail bed and nail matrix were more commonly detected in healthy children and no difference was present between psoriasis patients with abnormal or normal nail examination. Lack of standardization in scanning techniques as well as different scoring systems employed likely account for these results, highlighting the need for a standardized nail ultrasound protocol.

This pilot study was limited due to the small sample size and cross-sectional design. However, an exclusion of patients with psoriasis treated with systemic medications eliminated the potentially joint-protective effect of these therapies as a confounder. Not surprisingly, the majority of the patient population had mild psoriasis, as individuals with more severe disease are more likely to be receiving systemic treatment and thus were excluded from the study. Additionally, only finger, knee, and ankle joints were evaluated by MSUS in this study for feasibility since these joints are the most common locations affected by joint inflammation in psoriasis reported in the literature [11]. A comprehensive scanning approach involving more joints for MSUS may provide additional findings in future studies. The inclusion of a healthy control population was an important strength. Furthermore, all participants were evaluated by standardized physical and ultrasound examinations and their results remained blind to each other during the scoring of the ultrasound findings. Although validated pediatric-specific MSUS definitions and scoring systems for synovitis were used in this study to define the presence and extent of pathology at the level of the finger, knee, and ankle joints [18, 19], larger studies confirming the validity of these MSUS scoring systems in children and standardized definitions of nail ultrasound in children are needed [27]. Additionally, OMERACT enthesitis definitions were employed in this investigation but have not been formally validated in pediatric populations and pediatric normative data are lacking. Future studies in healthy children may help to explain PD positivity in the lack of B-mode entheseal findings detected in this study.

Conclusions

This is one of the first investigations detailing MSUS findings of the joints, entheses, and nails in pediatric psoriasis patients. Our psoriasis cohort was found to have subclinical synovitis in the finger, knee, and ankle joints, as well as present with abnormal nail structure more frequently compared to healthy controls. The distribution of subclinical synovitis across multiple locations rather than a significant predominance of a single involved joint may correspond with the heterogenous presentation of juvenile psoriatic arthritis. Larger longitudinal studies may help to delineate the temporal relationship between skin and joint disease and the role of ultrasound in the early detection and diagnosis of joint inflammation in children with psoriasis. Furthermore, ultrasound enhances the assessment of nail unit structures and the classification of nail plate morphology in psoriasis which could have a role in the characterization of the disease.

Supplementary Information

Below is the link to the electronic supplementary material.

Abbreviations

BMI

Body mass index

CARRA

Childhood Arthritis and Rheumatology Research Alliance

DIP

Distal interphalangeal

ILAR

International League of Associations for Rheumatology

IQR

Interquartile range

JIA

Juvenile idiopathic arthritis

JPsA

Juvenile psoriatic arthritis

MCP

Metacarpophalangeal

MSUS

Musculoskeletal ultrasonography

NAPSI

Nail Psoriasis Severity Index

NSAID

Non-steroidal anti-inflammatory drug

OMERACT

Outcome Measures in Rheumatology

PASI

Psoriasis Area and Severity Index

PD

Power Doppler

PIP

Proximal interphalangeal

PRCSG

Pediatric Rheumatology Collaborative Study Group

PROMIS

Patient-Reported Outcomes Measurement Information System

PsA

Psoriatic arthritis

SD

Standard deviation

Author contributions

LN, TVT, CB, and PVF contributed to the study design and data collection. The first draft of the manuscript was written by LN and POAA. All co-authors participated in the data interpretation, commented on previous versions, and approved the last version of the manuscript.

Funding

National Institutes of Arthritis and Musculoskeletal Skin Diseases under Award - Number P30AR076316. Dr. Vega-Fernandez was supported by the National Institutes of Arthritis and Musculoskeletal Skin Diseases under Award - Number K23AR081424A. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

Data availability

Data will be shared upon reasonable request to the corresponding author.

Declarations

Ethics approval and consent to participate

The study was approved by the Institutional Review Board of Cincinnati Children’s Hospital Medical Center (IRB# 2021 − 0756) and was conducted in accordance with the Declaration of Helsinki. All patients and parents provided their written informed consent for this study.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.