Background Polymyalgia Rheumatica (PMR) is an inflammatory disease which does not have specific diagnostic tests or pathological symptoms and is defined with clinical characteristics. Among the acute phase reactants (APR), erythrocyte sedimentation rate (ESR) and C-Reactive Protein (CRP) are laboratory findings used in the diagnosis and follow-up. Although abnormal ESR and CRP levels are included in the criteria for the classification of PMR, ESR and CRP can be observed as normal in 13% of PMR patients.

Objectives In the study, it was aimed to determine the incidence of normal APR rates in patients diagnosed with PMR and to identify the distinguishing characteristics of these patients.

Methods PMR patients who were clinically diagnosed at a single center were reviewed. After the presence of bursitis was demonstrated with ultrasonography (USG) in patients with normal ESR and CRP rates, they were accepted to have PMR. Patients with normal rates of ESR and CRP were compared against patients with high levels of ESR and/or CRP.

Results In all 54 patients who were diagnosed with PMR (63% female, and mean age 65.39±7.39 years), >45 minute morning stiffness was present. Symptom duration median (IQR) was 3.5 (3) months, and ESR and CRP were found to be high in 72.2% and 83.3% of the patients, respectively. ESR and CRP were normal in 8 patients (14%), and serum amyloid A (SAA) was determined to be high in all these patients. At the time of the diagnosis, 51 patients (94%) had shoulder pain, and 41 patients (75%) suffered from hip pain. At the time of the diagnosis, median (IQR) ESR was found as 59.5 (49) mm/hour and CRP as 16.25 (38) mg/L. In 20 patients, SAA median (IQR) was 36 (26) U/L. The initial median (IQR) steroid dosage at the beginning of the treatment was prednisolone 20 mg/day. As steroid sparing therapy, methotrexate was started in 27 patients, and azathioprine was started in 4 patients.

In the group with normal levels of ESR and CRP, diagnosis median (IQR) ESR was 28 (4) mm/hour and CRP was 3.9 (1) mg/L, while in the group with high levels of ESR and CRP, diagnosis median (IQR) ESR was 76.5 (26) mm/hour, and CRP was 35.5 (60) mg/L. When the groups with normal and high levels of ESR and CRP were compared, it was found that diagnosis age was lower (p=0.027) in the normal ESR and CRP group, while the symptom duration was longer (p<0.001). When the patients were evaluated in terms of presence of at least one comorbidity, comorbidity was determined to be significantly lower in this group (p=0.01). Rheumatoid factor positivity, presence of anemia, and platelet count at the time of diagnosis and PMR exacerbation and giant cell arthritis development in the follow-up were similar.

In the multiple regression analysis, when diagnosis age, symptom duration, and comorbidity were evaluated together, long symptom duration was independently associated with PMR with ESR and CRP normal levels (OR=0.045, %95 CI 0.03-0.676, p=0.025).

*SAA was measured in 20 patients.

Conclusion Significantly younger age of diagnosis, longer symptom duration and less comorbidity were determined in the group with normal levels of ESR and CRP compared to the group with high levels of ESR and CRP. While bursitis can be demonstrated with USG in patients who are clinically evaluated to have PMR, APRs such as SAA other than ESR and CRP can also be used.

REFERENCES:

NIL.

Acknowledgements: NIL.

Disclosure of Interests None Declared.

Keywords: Vasculitis, Diagnostic tests, Real-world evidence

DOI: 10.1136/annrheumdis-2023-eular.2056