Patients
Fifteen patients with PsA, 5 with RA, and 5 healthy control persons (CTRLs) were examined with US, contrast-enhanced MRI, x-ray, and clinical assessment. The PsA and RA patients were required to have at least one clinically affected finger joint or dactylitis to enter the study. The PsA group included 11 women and 4 men with a median age of 57 years (range 39 to 79) and a median disease duration of 3 years (range 0 to 24). They had a median of 5 tender joints (range 1 to 24) and 2 swollen joints (range 1 to 10). The RA group comprised 5 women with a median age of 48 years (range 32 to 60) and a median disease duration of 7 years (range 0 to 15). Their median tender and swollen joint counts were 8 (range 3 to 9) and 6 (range 2 to 11), respectively. All 5 CTRLs (4 women and 1 man with a median age of 63 years; range 35 to 71) had no prior history of rheumatological disease and no clinically affected joints at inclusion. The study participants signed consent forms after receiving oral and written information. The study was approved by the local Danish ethics committee.
Ultrasonography
US was performed with a GE LOGIQ 9 unit (General Electric Medical Systems, now known as GE Healthcare, Little Chalfont, Buckinghamshire, UK) using a high-frequency 9- to 14-MHz linear array transducer. All persons were examined by the same trained ultrasonographer (CW = US1) and examination was repeated in 8 persons (6 PsA, 1 RA, and 1 CTRL) by another trained ultrasonographer (MS = US2), and both US1 and US2 have a rheumatological background (Figure 1). US2 was blinded to diagnosis and clinical data, and both were blinded to other imaging findings, including the sonographic findings of the other ultrasonographer. Bilateral 2nd–5th metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints and 1st–5th metatarsophalangeal (MTP) joints were assessed with US for inflammatory changes: synovitis (synovial hypertrophy and/or effusion and/or power Doppler [PD] signal) and capsular/extracapsular PD signal (only in PIP joints) (Figure 2). Furthermore, the tendons of the fingers (2nd–5th flexor and extensor tendons) were assessed for insertional changes (edema and/or calcification and/or periosteal changes and/or PD signal) and tenosynovitis. Finally, all joints were assessed for bone changes: bone erosions and bone proliferations. The presence or absence of each parameter was noted. The palmar and dorsal aspects of each joint were examined in a longitudinal plane. A transverse view was added in case of doubt concerning the type of the detected finding or for confirmation of an erosion. Additional views were radial view of the 2nd MCP joint, ulnar view of the 5th MCP joint, radial and ulnar views of all PIP joints, medial view of the 1st MTP joint, and lateral view of the 5th MTP joint. All views were obtained with the hands and feet in a neutral position. Mild synovitis in joints (score 1 according to the scoring system proposed by Szkudlarek and colleagues [10] for MCP and MTP joints) and a small amount of fluid in the tendon sheath below the flexor tendons at the palmar side of the PIP joints were considered a normal finding. A small amount of fluid around the fat pad on the palmar side of the PIP joint and a synovial membrane thickness below 12 mm (measured at the site of maximal thickness) of the DIP joints were also considered normal (based on unpublished data from CTRLs by Wiell and colleagues). The following US definitions were employed: bone erosion = bone cortex discontinuation in the area adjacent to the joint, visualized in two planes; bone proliferation = bone cortex proliferation in the area adjacent to the joint; synovitis = anechoic or hypoechoic intracapsular area, different from cartilage with or without PD signal; tenosynovitis = hypoechoic rim around the flexor tendon with or without PD signal; capsular/extracapsular changes = PD signal (intracapsular and/or extracapsular at the insertion of capsule or ligament) at the radial or ulnar sides of the PIP joints, different from nutritious vessels; and insertional changes = intratendinous hypoechoic enlargement and/or intratendinous hyperechoic bands with or without acoustic shadow and/or periosteal irregularities and/or intratendinous PD signal at the entheses.
Ultrasonography parameters
The setting for grey-scale US was 14 MHz, and the pulse repetition frequency for the PD signal was set at 500 Hz.
Magnetic resonance imaging
MRI was performed on a Philips Panorama 0.6 tesla unit (Philips Medical Systems, Helsinki, Finland) using a three-channel phased-array solenoid coil within 2 days of the US. The more clinically affected hand (2nd–5th MCP, PIP, and DIP joints) was assessed for the presence or absence of aforementioned changes by a radiologist experienced in musculoskeletal radiography (MH), who was blinded to clinical and other imaging findings.
Magnetic resonance imaging parameters
The acquired images included a coronal T1-weighted three-dimensional fast field echo (repetition time [TR] 20 ms, echo time [TE] 8 ms, flip angle 25°, field of view [FOV] 120 mm, matrix 240 × 240, slice thickness [ST] 0.8 mm, number of acquisitions [Acq] 1, and acquisition time [TA] 4.31 minutes) and axial fat saturated T1-weighted (TR 31 ms, TE 11 ms, flip angle 25°, FOV 150 mm, matrix 256 × 256, ST 4 mm, Acq 1, and TA 4.57 minutes) sequences before and after intravenous administration of the contrast agent Omniscan (0.1 mmol/kg; Amersham Health AS, now part of GE Healthcare). Additionally, sagittal (TR 4,000 ms, TE 17 ms, inversion time [TI] 80 ms, flip angle 90°, FOV 160 mm, matrix 256 × 256, ST 3 mm, Acq 1, and TA 6.56 minutes) and axial (TR 3,000 ms, TE 17 ms, TI 80 ms, flip angle 90°, FOV 160 mm, matrix 256 × 256, ST 3 mm, Acq 1, and TA 7.01 minutes) short tau inversion recovery (STIR) sequences were performed before contrast administration. Reconstructions were performed with a ST that was half of the acquired ST.
Projection radiography
X-ray of hands and feet in a posterior-anterior projection was performed within a month of the US. X-rays of both hands and feet (2nd–5th MCP, PIP, DIP, and MTP joints) were assessed for bone erosions and bone proliferations according to the Ratingen scoring system [11] by an experienced musculoskeletal radiologist (AV) blinded to clinical and other imaging findings.
Clinical examination
All 25 persons underwent clinical examination prior to US to determine the presence or absence of swelling and/or tenderness of the finger and MTP joints (in all 34 joints per person). One patient with PsA had had joint replacement in 4 MCP joints and total anchylosis in one PIP joint. These joints were not assessed.
Statistical analysis
Absolute agreements and unweighted kappa values between US (US1), MRI, x-ray, and clinical examination were calculated. Furthermore, the interobserver agreement between US1 and US2 was determined. Kappa values below 0.20 were considered poor, 0.21 to 0.40 fair, 0.41 to 0.60 moderate, 0.61 to 0.80 good, and 0.81 to 1.00 very good [12]. MRI was used as the standard reference method for the calculation of the sensitivity and specificity of US, x-ray, and clinical examination [12]. The statistical software used was SPSS version 12.0 for Windows (SPSS Inc., Chicago, IL, USA).