Polymyalgia rheumatica (PMR) is an inflammatory condition causing muscle pain and stiffness, primarily affecting large muscle groups around the shoulders and hips. Diagnosing PMR involves assessing various factors, as no single test confirms its presence. A timely diagnosis is important for effective management.
Initial Patient Evaluation
The diagnostic process begins with a thorough evaluation of the patient’s medical history and a physical examination. Healthcare providers look for characteristic symptoms, such as sudden onset pain and stiffness, often appearing on both sides of the body, particularly in the shoulders, neck, and hips. This stiffness is most pronounced in the morning, lasting longer than 45 minutes. Patients might describe difficulty with daily activities like getting dressed or rising from a chair.
During the physical examination, a doctor assesses the range of motion in affected areas and checks for tenderness. While patients may report generalized weakness due to pain, true muscle weakness is not a feature of PMR. These initial symptoms guide further investigation to distinguish PMR from other musculoskeletal or inflammatory conditions.
Blood Test Indicators
Blood tests support a PMR diagnosis and help rule out other conditions. Two key inflammatory markers, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), are elevated in individuals with PMR. ESR measures how quickly red blood cells settle, indicating inflammation, while CRP is a more sensitive indicator of current disease activity. While elevated, these markers are not specific to PMR and can be high in various inflammatory conditions.
A complete blood count (CBC) may reveal mild normocytic anemia, a type of anemia associated with chronic inflammation, and sometimes a mild elevation in platelet count (thrombocytosis). To differentiate PMR from other autoimmune conditions like rheumatoid arthritis, tests for rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies are done; these are negative in PMR. Liver, kidney, and thyroid function tests are also done to assess overall health and exclude other causes of symptoms.
Ruling Out Other Conditions
Distinguishing PMR from other conditions is important in diagnosis because its symptoms can mimic many ailments. Rheumatoid arthritis (RA), for example, also causes joint pain and stiffness, but it affects smaller joints in the hands and feet, often leading to visible joint swelling, and is characterized by positive RF or anti-CCP antibodies. Osteoarthritis, a degenerative joint disease, involves different pain patterns and does not present with elevated inflammatory markers. Hypothyroidism can cause fatigue and muscle aches, but blood tests for thyroid hormones show distinct abnormalities.
Infections can lead to widespread body aches and elevated inflammatory markers, requiring careful clinical assessment. Rarely, PMR-like symptoms can be a paraneoplastic syndrome, an indirect effect of an underlying malignancy. Atypical features like significant weight loss, night pain, or asymmetric symptoms might prompt cancer screening.
Giant Cell Arteritis (GCA), an inflammatory condition of blood vessels, is closely associated with PMR. Approximately 10% to 20% of individuals with PMR may also develop GCA, and conversely, up to 50% of GCA patients experience PMR symptoms. Symptoms of GCA, such as new headaches, jaw pain with chewing, vision changes (e.g., blurred or double vision), or scalp tenderness, require immediate medical attention due to the risk of permanent vision loss or stroke.
Advanced Diagnostic Tools
While clinical assessment and blood tests are key, advanced diagnostic tools may be used in specific situations to aid PMR diagnosis or exclude other conditions. Imaging techniques like ultrasound or magnetic resonance imaging (MRI) are not routinely used for PMR itself. However, they can be helpful in ruling out other joint or soft tissue problems that might present with similar symptoms. These imaging modalities may also reveal inflammatory changes in bursae or tendons, which can support a PMR diagnosis.
A temporal artery biopsy is the definitive test for diagnosing Giant Cell Arteritis (GCA), but it is not performed to diagnose PMR directly. This procedure involves taking a small sample of the temporal artery, located near the temple, for microscopic examination to detect inflammation. If GCA is strongly suspected alongside PMR symptoms, treatment may be initiated immediately, even before biopsy results are available, due to the urgency of preventing potential vision loss.
Confirming the Diagnosis
The diagnosis of polymyalgia rheumatica is largely a clinical one, often considered a “diagnosis of exclusion.” This means a healthcare provider combines the characteristic pattern of symptoms, elevated inflammatory markers from blood tests, and the careful exclusion of other conditions. Established classification criteria guide clinicians, emphasizing age over 50 years, bilateral shoulder pain, and abnormal inflammatory markers.
A rapid response to a low-dose corticosteroid, such as prednisone, is a strong diagnostic feature. Patients experience significant relief from pain and stiffness within a few days of starting treatment, often within 1 to 3 days. This swift improvement helps confirm the diagnosis and guides the long-term management plan. Ongoing monitoring is necessary to adjust medication and watch for potential complications or the development of associated conditions like GCA.