Polymyalgia Rheumatica (PMR) is a common inflammatory disorder that primarily affects adults over the age of 50. This condition causes widespread aching and stiffness, particularly in the large muscle groups near the torso. Diagnosing PMR can be challenging because no single laboratory test can definitively confirm its presence. Instead, the diagnosis is clinical, relying on a combination of a patient’s specific symptoms, blood test results, and the exclusion of other diseases that can mimic its presentation.
Recognizing the Characteristic Symptoms
Diagnosis begins with the patient’s clinical history and physical examination. The defining features are pain and stiffness that are symmetrically distributed across the body. This discomfort is concentrated in the shoulder girdle (shoulders, neck, and upper arms) and the pelvic girdle (hips, thighs, and buttocks).
The stiffness is characteristically worst in the morning or after periods of rest. For doctors to suspect PMR, this morning stiffness must typically persist for longer than 45 minutes. Patients often report difficulty with daily tasks, such as raising their arms, getting out of bed, or standing up from a seated position. These localized symptoms are frequently accompanied by systemic signs of inflammation, including unexplained fatigue, low-grade fever, loss of appetite, and unintended weight loss.
The Role of Inflammatory Markers
Once PMR is suspected based on clinical presentation, blood tests are ordered to look for evidence of systemic inflammation. The two most important laboratory markers are the Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP). The ESR measures the rate at which red blood cells settle, while the CRP measures a protein released by the liver in response to inflammation.
Levels of both the ESR and CRP are typically significantly elevated, supporting the diagnosis of an inflammatory process. CRP is often considered a more sensitive indicator of active inflammation because it is less affected by factors like increasing age. However, these markers are not specific to PMR; high levels only confirm inflammation is present. Furthermore, in 5 to 20% of PMR cases, both the ESR and CRP levels may be within the normal range, particularly early in the disease.
Differential Diagnosis: Excluding PMR Mimics
A core principle in PMR diagnosis is that it is a diagnosis of exclusion, meaning other conditions must be carefully ruled out before a final determination is made. Many diseases present with similar pain, stiffness, and elevated inflammatory markers, making this the most complex diagnostic step. Doctors must exclude rheumatological disorders like late-onset Rheumatoid Arthritis (RA), infections, muscle diseases such as polymyositis, and certain types of cancer.
To eliminate these mimics, specialized blood tests are performed. Tests for Rheumatoid Factor (RF) and anti-cyclic citrullinated peptide antibodies (anti-CCP) help rule out RA, as these are typically absent in PMR. Muscle enzyme tests, such as Creatine Kinase (CK), are checked; elevated CK levels suggest a muscle disorder like myositis, while they remain normal in PMR. Thyroid function tests are also performed, as thyroid dysfunction can cause muscle pain.
Imaging studies, such as ultrasound, may be employed to look for inflammatory findings common in PMR, like bursitis or tenosynovitis in the shoulders and hips. A serious condition that must be excluded is Giant Cell Arteritis (GCA), which can occur alongside PMR and requires immediate, high-dose treatment due to the risk of vision loss.
The Final Diagnostic Step: Response to Treatment
The final and often definitive component of the diagnostic process is the therapeutic trial, which observes the patient’s reaction to medication. PMR is known for its dramatic and rapid response to low doses of glucocorticoids. A doctor will typically prescribe a small, targeted daily dose of an oral glucocorticoid, such as prednisone, to gauge the effect on the patient’s symptoms.
A rapid and substantial improvement in pain and stiffness, frequently noted within 24 to 72 hours of starting the medication, strongly supports the diagnosis of PMR. Failure to achieve a noticeable, sustained response to the initial low-dose treatment prompts the doctor to re-evaluate for a different condition. This therapeutic response is so characteristic that formal classification systems, such as the 2012 criteria developed by EULAR and ACR, incorporate a rapid response to glucocorticoids as a factor in the overall assessment.