The exact etiology of PMR is undetermined, but it is believed to be in the same spectrum of disease as giant cell arteritis (GCA) because the same family of HLA serotypes, HLA-DR4, is affected in both. Like other autoimmune conditions, in PMR, there is likely interplay between genetic and environmental factors causing a dysregulation of the immune system.
The European League Against Rheumatism (EULAR) / American College of Rheumatology (ACR) 2012 provisional classification criteria for PMR are:
- Patient is 50 years or older
- Bilateral shoulder pain is not better explained by an alternative diagnosis
- Presence of morning stiffness for more than 45 minutes
- Elevated levels of C-reactive protein (CRP) and/or erythrocyte sedimentation rate (ESR)
- New hip pain
Diagnosis of PMR is generally made on clinical grounds. The patient can present with slow, subacute or chronic symptoms of malaise, fever, weight loss, night sweats, and anorexia. Pain and stiffness, rather than weakness, are common presenting symptoms and generally involve the upper arms, posterior neck, lumbar region, and / or pelvic girdle.
Magnetic resonance imaging (MRI) and ultrasonography are equally effective in confirming PMR. Common shoulder lesions in PMR are subacromial or subdeltoid bursitis. Some patients present with "benign synovitis," which on ultrasound will not demonstrate true joint erosions. Glenohumeral joint synovitis and long-head biceps tenosynovitis can also coexist in PMR.
A patient's rapid response to corticosteroids may help confirm the diagnosis of PMR (steroids will decrease the pain associated with other inflammatory conditions as well).
PMR and GCA:
GCA is a systemic vasculitis affecting medium- to large-sized arteries, including the aorta and the extracranial branches of the carotid artery. PMR and GCA have a significant clinical association: 16%-21% of cases of PMR are associated with GCA, and 40%-60% of patients diagnosed with GCA also have PMR.