Chronic but not inflammatory changes at the Achilles' tendon differentiate patients with peripheral spondyloarthritis from other diagnoses - Results from a prospective clinical trial

Abstract

Background: Imaging has an essential role in the new spondyloarthritis (SpA) classification criteria for axial but not for peripheral manifestations. We evaluated the impact of imaging findings for identification and treatment decisions in patients with peripheral spondyloarthritis (pSpA) and controls (non-SpA).

Methods: Patients with pSpA (Assessment of SpA international Society criteria, n=30) and non-SpA (n=30), aged <45 years, with painful heels or knees, were recruited. Conventional radiography, grey-scale ultrasound including power Doppler (US/PDUS) and MRI of symptomatic areas were performed to assess inflammatory and structural changes. Mann-Whitney U test was used for group comparisons.

Results: In total, 105 painful entheses (71 heels, 34 knees) in 60 patients were examined. Differences between diagnoses were found for symptom duration (pSpA: 17.2±27.5 vs non-SpA: 4.4±4.3 months), human leucocyte antigen B27 prevalence (67% vs 13%) and gender distribution (53.3% vs 20% male, respectively), all P<0.05. Logistic regression analysis for baseline differences showed that chronic changes (erosions and calcification) in the heel were more frequent in pSpA versus non-SpA by US/PDUS (62.5% vs 28.6% patients and 59.5% vs 26.5% entheses, P<0.05). Inflammatory changes in heel or knee by US/PDUS and MRI could not differentiate between non-SpA and pSpA.

Conclusions: Differentiation between pSpA and non-SpA was only possible based on structural but not inflammatory changes in the heels and knees of symptomatic patients. US/PDUS was superior to MRI for this purpose. These findings imply that pSpA is associated with erosive changes at enthesitic sites, while inflammation and susceptibility are of minor influence for the development of erosions and calcification to pSpA.

Keywords: magnetic resonance imaging; spondyloarthritis; ultrasonography.

Figure 1

Example of pathological MRI (T1-weighted sequence after gadolinium) of the ankle from a patient with peripheral spondyloarthritis (female, 46 years). ‘O’, tendinitis; *, bone marrow oedema; fat arrow, sub-Achillean bursitis; thin arrow, oedema in the tendon of the plantar aponeurosis, in this case due to a plantar spur.

Figure 2

(A) Detailed comparison of the prevalence of single pathological lesions in both heel and knee in patients with SpA and non-SpA patients, as assessed by PD and MRI for both inflammatory and chronic changes. *P=0.008. (B) Detailed comparison of the prevalence of pathological lesions on a per patient basis in both heel and knee in patients with SpA and non-SpA, as assessed by PD and MRI for both inflammatory and chronic changes.*P=0.036. CHR, chronic structural lesion; INF, inflammatory lesion; PD, power Doppler; PDUS, power Doppler ultrasound; pSpA, peripheral spondyloarthritis; SpA, spondyloarthritis.

Figure 3

Prevalence of any pathological finding for inflammation (intratendinous or peritendinous inflammatory signal, bone marrow oedema at the painful sites) or chronic (thickness of painful tendon, pathological finding of fibrous structure including rupture of the painful tendon, bone erosion or calcification/enthesophyte formation at the site of examination) changes in the lower limbs (heel and knee) between patients with SpA and no SpA. The numbers given are proportions of sites being positive for inflammatory or chronic changes in PD and MRI in both heel and knee. Overall, only the difference between pSpA and non-SpA for chronic changes as assessed by PD was statistically significant. This finding was mainly based on the difference for bone erosions at the insertion of the Achilles’ tendon. PD, power Doppler; PDUS, power Doppler ultrasound; pSpA, peripheral spondyloarthritis; SpA, spondyloarthritis.