Dermatologica Sinica

ORIGINAL ARTICLE
Year
: 2021  |  Volume : 39  |  Issue : 1  |  Page : 27--32

Correlation of clinical diagnosis of dactylitis by the dermatologist and ultrasonographic diagnosis by the rheumatologist in patients with psoriasis arthritis: Experience of a single clinic


Yang Lo1, Ting- Shun Wang2, Ko- Jen Li3, Tsen- Fang Tsai2,  
1 Department of Dermatology, Cathay General Hospital, Taipei, Taiwan
2 Department of Dermatology, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
3 Division of Rheumatology, Immunology and Allergy, National Taiwan University Hospital, Department of Internal Medicine, Taipei, Taiwan

Correspondence Address:
Ko- Jen Li
Division of Rheumatology, Immunology and Allergy, National Taiwan University Hospital, Department of Internal Medicine, Taipei
Taiwan
Dr. Tsen- Fang Tsai
Department of Dermatology, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei
Taiwan

Abstract

Background: Dactylitis is a characteristic feature of psoriatic arthritis (PsA). However, early diagnosis of mild dactylitis is challenging and image examination, such as ultrasonography (US), can be helpful. Objectives: We aimed to compare the clinical diagnosis of dactylitis made by the dermatologist and ultrasonographic diagnosis by the rheumatologist. Methods: Consecutive patients diagnosed with peripheral PsA seen in the dermatologic clinics were referred to the same dermatologist for evaluation of dactylitis. Consecutive patients with and without clinical dactylitis were diagnosed in 19 and 19 patients, respectively, by the referred dermatologist. All patients were then referred to an experienced rheumatologist unaware of the clinical diagnosis for sonographic examination of all 20 digits. Dactylitis under US was diagnosed when both proximal and distal parts of a digit were at least 0.25 mm larger than the contralateral digit. Results: For the clinical dactylitis group, 7 (36.8%) patients had more dactylitis diagnosed by US than clinically, and 2 (10.5%) patients had no dactylitis diagnosed by US. For the clinically no dactylitis group, 4 (21.1%) patients had no diagnosis of dactylitis by US, and most of these patients (78.9%) were diagnosed with dactylitis under US by the rheumatologist. More digits affected by dactylitis were found for both groups, although no statistically significant differences were found, probably due to the small sample size. Conclusion: The results revealed concordance between the dermatologist and rheumatologist for clinical dactylitis but not for patients without dactylitis. For PsA patients, US is more sensitive and useful for early dactylitis diagnosis in a dermatologic clinic.



How to cite this article:
Lo Y, Wang TS, Li KJ, Tsai TF. Correlation of clinical diagnosis of dactylitis by the dermatologist and ultrasonographic diagnosis by the rheumatologist in patients with psoriasis arthritis: Experience of a single clinic.Dermatol Sin 2021;39:27-32


How to cite this URL:
Lo Y, Wang TS, Li KJ, Tsai TF. Correlation of clinical diagnosis of dactylitis by the dermatologist and ultrasonographic diagnosis by the rheumatologist in patients with psoriasis arthritis: Experience of a single clinic. Dermatol Sin [serial online] 2021 [cited 2021 Aug 3 ];39:27-32
Available from: https://www.dermsinica.org/text.asp?2021/39/1/27/311841


Full Text



 Introduction



Psoriatic arthritis (PsA) is a chronic, systemic inflammatory disease occurring in 10%–30% of patients with psoriasis.[1],[2] The prevalence of PsA seemed low in Asians but has been increasing recently.[3],[4] Possible explanations include underdiagnosis due to unfamiliarity of the symptoms and signs of PsA, changes in the diagnostic criteria of PsA, and westernization of lifestyles, which can increase the risk factors such as obesity and metabolic syndrome.[3] Dactylitis, sausage-like digits in appearance, refers to full-thickness inflammation of the digits and is a characteristic finding of PsA. In patients with PsA, the prevalence of dactylitis ranges from 20 to 58%.[5],[6] Dactylitis can also precede the occurrence of other features of PsA[7] and may be ignored by the patients.[5] Timely diagnosis of dactylitis is important because the presence of dactylitis has been associated with greater disease activity, less likelihood of minimal disease activity,[8] and earlier radiographic progression.[9] Magnetic resonance imaging (MRI) and ultrasonography (US) are both useful tools to detect PsA.[10],[11] Compared with MRI, US provides the advantage of ease to perform at lower cost and multiple joints at different body areas can be assessed at the same time.[12] However, the concordance rates between dermatologists and rheumatologists were lowest for dactylitis among the different domains of PsA.[13],[14] In these studies, the diagnosis of dactylitis was based mainly on physical examinations. Cold dactylitis, defined as diffuse swelling of the digits without tender sensation,[5] is sometimes difficult to detect. Thus, the aim of this study was to compare the clinical and sonographic examination in PsA patients with and without clinical diagnosis of cold dactylitis.

 Materials and Methods



Study cohort and clinical evaluation

Between May 2016 and March 2018, consecutive patients who had been diagnosed with PsA with active peripheral joints were referred to the dermatologist. Patients with frank red swollen digits were excluded for the purpose of blinding by the rheumatologist. A total of 19 patients were diagnosed with clinical dactylitis, while the controls comprised 19 unrelated patients without clinical dactylitis. Demographic data included the patient's age, gender, age of onset of psoriasis and PsA, family history, comorbidities, total tender and swollen joint counts, previous and current treatment and biologics use, body surface area of psoriasis, Psoriasis Area and Severity Index (PASI), C-reactive protein (CRP) level, erythrocyte sedimentation rate level, presence of antinuclear antibody (ANA), presence of rheumatoid factor, presence of human leukocyte antigen (HLA)-B27, and location of dactylitis. Biopsies were performed in selected cases to confirm the diagnosis of psoriasis. PsA was diagnosed according to the Classification Criteria for PsA criteria and confirmed by rheumatologists. The diagnosis of dactylitis was made based on the local tenderness and uniform swelling of the whole digits between the metacarpophalangeal and proximal interphalangeal, proximal, and distal interphalangeal joints[15] compared with the opposite digit by a young dermatologist who had been board certified for 3 years at the time of study initiation. After the clinical diagnosis of dactylitis by the dermatologist, US scans were scheduled and performed by an experienced rheumatologist, who performed the US without knowing the clinical diagnosis made by the dermatologist. To minimize the possible bias from clinical appearance, all of the digits were examined with US, and the diagnosis made by the rheumatologist was merely by the results of US. Dactylitis under US was defined as both the proximal and distal parts of a digit being larger than the digit on the contralateral side by more than 0.25 mm, which was modified from the previous study using Leeds dactylitis instrument (LDI).[16] The difference of 10% circumference between the affected digit and the contralateral site was defined dactylitis by LDI. Besides, according to one previous study, subcutaneous soft-tissue enlargement is presented in all patients with dactylitis.[17] Due to the high sensitivity for subcutaneous soft-tissue enlargement in detecting dactylitis by US, the comparison of the soft-tissue thickness enlargement of affected and contralateral sites was made. We set the cutoff number as 0.25 mm due to the smallest digit is approximately 2.5–2.7 mm in our patients. The scans were conducted using a broadband 7.2–14 MHz linear array transducer (Toshiba Xario XG ultrasound system, Tokyo, Japan). The study was approved by the local investigational research bureau of National Taiwan University Hospital (approval number: 201603042RIND). Written informed consent was obtained from each patient before enrollment.

Statistical analysis

Statistical analysis was performed using the SPSS 22.0 software (SPSS Inc., Chicago, IL, USA). Demographic data and clinical characteristics were summarized as the mean ± standard deviation (SD) for continuous variables. For categorical variables, proportions were described as percentages. Comparisons of two groups were made using the Pearson's Chi-square test for noncontinuous variables. P < 0.05 was regarded as statistically significant.

 Results



Study population

We identified 38 patients (47.4% male) who met the inclusion criteria in the study. The demographics of our study population are shown in [Table 1]. All patients had chronic plaque- type psoriasis and PsA. The mean age at presentation of psoriasis was 38.28 ± 15.95 years (mean ± SD). Among the two groups, the mean age at presentation of psoriasis for the study group and the control group was 40.42 ± 14.33 and 36.14 ± 17.55 years (mean ± SD), respectively. The mean age at presentation of PsA was 47.95 ± 14.09 and 45.53 ± 16.35 years, respectively. Moreover, the mean interval between psoriasis and PsA was 7.27 ± 8.77 and 9.38 ± 7.55 years, respectively. The majority of the patients in the clinical dactylitis group presented with psoriasis first (68.4%), and 6 (31.6%) patients presented with psoriasis and PsA concurrently during the same calendar year. Most of the patients without clinical dactylitis also presented with psoriasis first (84.2%), and 3 (15.8%) patients presented with psoriasis and PsA concurrently during the same calendar year. The baseline number of swelling and tender joints was 3.26 ± 2.42 and 4.90 ± 7.72 for the clinical dactylitis group and 3.37 ± 3.34 and 4.26 ± 4.51 for the clinically no dactylitis group, respectively. The baseline PASI was 5.83 ± 3.93 and 4.68 ± 6.48, respectively. The CPR level was 0.55 ± 0.76 and 0.27 ± 0.37, respectively. Eleven (28.9%) patients had been treated with biologic agents. Ten (26.3%) patients had family history of psoriasis. Four (10.5%) patients had ANA positivity, none of the patients had HLA-B27 positivity, and rheumatic factor was detected only in one patient. For the clinical dactylitis group, 10 (52.6%) patients had dactylitis in the fingers, and 9 (47.4%) had dactylitis affecting the toes. Ten (26.3%) patients had left side affected, 8 (42.1%) patients had right side affected, and 1 patient had both sides affected. Five (26.3%) patients had dactylitis involving more than one digit. The most frequently affected digit in both hands was the third digit (middle finger), followed by the second digit (index finger). The fourth toe was the most often affected in the feet. The US findings are shown in [Table 2]. For the clinical dactylitis group, 7 (36.8%) patients had more dactylitis diagnosed by US than clinically, and 2 (10.5%) patients had no dactylitis by US. For the clinically no dactylitis group, 4 (21.1%) patients showed no dactylitis by US; most of the patients (78.9%) were still diagnosed with dactylitis by the rheumatologist under US. More digits affected by dactylitis were found for both groups, although no statistical significant differences were found between the two groups, probably due to the small sample size. For the clinical dactylitis group, the digit numbers of dactylitis were 1.37 ± 0.68 by clinical examination and 1.68 ± 0.89 by US examination. For the clinically no dactylitis group, the digit numbers of dactylitis were 1.26 ± 0.99 by US examination.{Table 1}{Table 2}

 Discussion



PsA occurs in 30% of patients with moderate-to-severe psoriasis,[18] but an inconsistent relationship between the severity of the PsA and the extent of psoriasis was reported.[19] According to previous studies, greater body weight and more swollen joints were observed in patients with more extensive psoriasis.[20] Psoriasis typically appears prior to the onset of PsA,[21],[22] but nearly 15% of patients noticed joints symptoms first.[22] In our study, psoriasis appeared earlier than PsA in most of the patients, and nearly 30% of patients noticed joint and skin symptoms at the same time. Clinical overt swelling and tenderness of PsA can be preceded by asymptomatic joint inflammation, and image examination can be used to detect early PsA.[23] According to previous study, the key predictive factors for radiographic progression of PsA were male sex, high disease activities, and dactylitis.[9]

The pathogenesis of dactylitis was not clear. An ultrasound study performed by Kane et al. found flexor tenosynovitis in 24 of 25 dactylitic digits and joint synovitis in 52% of dactylitic digits; furthermore, subcutaneous edema was noted in all affected digits.[17] Diffuse osseous inflammation and osteitis at affected digits are the features of PsA.[24] A further power Doppler ultrasound study found soft-tissue thickening (termed “pseudotenosynovitis”) in 8 of 25 digits in the study.[25] Diffuse inflammation results in a sausage-like clinical appearance. Currently, entheses are considered the center of the disease, combined with spreading inflammation to the surroundings of articular areas.[26],[27] Furthermore, the interleukin (IL)-17 and IL-23 pathway, combined with trauma, might contribute to the formation of dactylitis,[28] and mechanical stress could amplify the inflammatory responses.[29] HLAB*2705 and HLAB*0801 have been reported to be linked to dactylitis.[30],[31]

The presence of dactylitis could be an important clue to early diagnosis of PsA.[32] Although swollen digits can be caused by other diseases, especially infection, the presence of dactylitis can help differentiate PsA from other types of inflammatory arthritis such as rheumatoid arthritis (RA) and osteoarthritis.[33] Usually, dactylitis can be easily recognized due to the red tender swelling of entire digit compared with the neighboring or contralateral digits,[34] but early diagnosis of mild forms of dactylitis can be challenging, especially in patients with cold dactylitis.[35]

The use of US for diagnosing PsA is gaining popularity nowadays, and several US scoring systems for dactylitis have been proposed.[36],[37],[38],[39],[40],[41],[42] However, the correlation between the US scores and patient global assessment of PsA was not always concordant.[35] The major differential diagnosis of PsA is RA, which could usually be differentiated by US.[43],[44] Extrasynovial changes may be remarkable for PsA patients but not for patients with RA.[43] The major findings of dactylitis by US scans include joint synovitis, soft tissue edema, and soft-tissue thickening.[37] The detection of soft tissue edema by US could be useful in early differential diagnosis of PsA and even in patients without clinical dactylitis.[44]

Based on previous study, the presence of tenderness with dactylitis was associated with higher synovitis grade, and earlier lesions are associated with extra synovial inflammatory changes.[37] Recently, a comparison of symptomatic dactylitis and asymptomatic dactylitis under US was reported. Interestingly, a greater prevalence of joint synovitis was found in patients with cold dactylitis than symptomatic dactylitis.[36] Furthermore, the accessory pulleys are thickened in PsA, especially for the established dactylitis compared with other arthritis.[38]

Several objective measurements for dactylitis have been developed, including circumference measurement.[16],[45] In our study, dactylitis was measured by the increased distance compared to the contralateral digit using US, which resembled the method from the Leeds Dactylitis Index that calculated the ratio of the circumference between the affected digit and the contralateral digit.[16],[46] The fourth toe was the most commonly affected digit in the feet in our study, which was consistent with a previous study.[47] The result was interesting because of the relatively small size of the fourth toe, which was less prone to trauma. On the other hand, the index finger was the most frequently affected finger on the same study,[47] possibly related to the trigger by trauma. Dactylitis was reported to affect right side more commonly than left side,[7] and affected toes more than fingers.[5],[7] Our result showed inconsistent results, possibly due to small patient numbers. US detects more involved digits in both groups. However, patients with clinical dactylitis had more digit swelling than the opposite toes compared with the other group, though without statistical significance. The results of our study revealed consistency between the dermatologist and rheumatologist for most patients with clinical dactylitis but not for patients without dactylitis. The result was consistent with a previous study showing that 70% of asymptomatic dactylitis still presents with ultrasound inflammatory abnormalities.[36] The subclinical US findings can be predictive for the progression of PsA based on the previous study.[48] Thus, for the dermatologist, when dealing with PsA patients, imaging is helpful for early diagnosis of dactylitis. The cooperation between dermatologists and rheumatologists for the comprehensive care for PsA is important.[49],[50]

The main limitation of this study was the small sample size. Second, due to the study conducted from 2016 to March 2018, the concept of A1 pulley related to the flexor tendon and dactylitis was not established at that time,[38] so the changes of A1 pulley thickening were not recorded by the US. The strength of this study was the reliable US results performed by an experienced rheumatologist and without knowing the diagnosis made by the dermatologist. Furthermore, only patients with cold dactylitis were included for the purpose of blinding. This study emphasizes the importance of US examination in detecting early subclinical dactylitis. In addition, the use of background treatment, including biologics, may modify the clinical and ultrasonographic findings of dactylitis.

 Conclusion



We tried to reveal the difference in diagnosis of dactylitis by a dermatologist and rheumatologist as assessed by clinical and US findings, respectively, in patients with PsA. This study illustrated the usefulness of US in the early diagnosis of dactylitis and the importance of dermatology-rheumatology cooperation in the management of PsA. Further larger studies are needed to determine long term outcomes of patients with only sonographic evidence of dactylitis.

Financial support and sponsorship

Nil.

Conflicts of interest

Prof. Tsen-Fang Tsai, a consultant editor of Dermatologica Sinica, had no role in the peer review process of or decision to publish this article.

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