Polymyalgia rheumatica (PMR) is a systemic inflammatory disease that affects elderly people. It is characterized by pain and morning stiffness in the shoulders, pelvic girdles and neck. Glucocorticoids are the mainstay of the treatment. In clinical practice, the disease activity of PMR and corresponding treatment changes are based on the presence of symptoms and inflammatory markers. The interpretation of these abnormalities can be surprisingly difficult, especially when they are not consistent. In 2004, Leeb and Bird developed a composite score for measurement of disease activity in PMR, called the polymyalgia rheumatica activity score. It consists of 5 domains: morning stiffness time, ability to elevate the upper limbs, physician's global assessment, pain and CRP level. However, high-quality evidence on the measurement properties is lacking and there is still no consensus on the optimal cut off point.

Based on a Delphi study with physicians and patients OMERACT defines laboratory markers of systemic inflammation, pain, stiffness and physical function as the four inner core of domains considered mandatory for clinical trials of PMR, most frequently measured by erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP), visual analogue scale (VAS) for pain, morning stiffness time and Health Assessment Questionnaire-Disability Index (HAQ-DI) respectively. Patient's global fatigue was strongly recommended to measure in PMR as well. Recently, a PMR-specific patient-reported outcome measure was developed, called the PMR impact scale. However, outcome measures in PMR studies lack consistency and there is no high-quality evidence on the measurement properties. In addition, the evolution of these patient reported outcomes is not known.

The primary objective of this prospective observational trial is to validate the PMR-activity score and to determine the optimal cut-off point to discriminate between disease remission and active disease. The secondary objective is to assess the evolution of the patient reported outcomes during the disease course and their relation with disease activity.

The investigators intend to perform a 12-month, observational prospective trial in patients with recently diagnosed PMR. Patients will be followed and treated as standard of care. Follow-up visits will be planned at 8 weeks, 16 weeks, 26 weeks and 52 weeks. As in standard of care, additional visits can be planned if necessary, e.g. in case of symptoms suggestive of relapse. Each visit ESR, CRP, morning stiffness time, ability to elevate the upper limbs, physician's global assessment and VAS for pain as components of the PMR-activity score and VAS for global health, pain, stiffness and fatigue, HAQ-DI, Short Form Health survey (SF36) and PMR impact scale as patient-reported outcomes will be collected.

Inclusion Criteria:

• Diagnosis of PMR based on the judgment of an experienced clinician (affiliated with the general internal medicine or rheumatology department), taking into account all available information (clinical symptoms, biochemical, radiological, and PET results)
• Able to give informed consent
• Understanding and able to write Dutch, English or French

Exclusion Criteria:

• Concomitant diagnosis of giant cell arteritis (new diagnosis or being treated for giant cell arteritis)
• Concurrent rheumatoid arthritis, other inflammatory arthritis or other connective tissue disease
• Patients on glucocorticoids or other immunosuppressive drugs for another indication

Diagnosis of PMR