Polymyalgia Rheumatica (PMR) is an inflammatory condition that causes widespread muscle pain and stiffness, primarily affecting the shoulders, neck, and hips. It almost exclusively affects people over the age of 50, with the average age of onset being around 70 years old. Diagnosis can be complex because no single test confirms PMR; instead, doctors must rely on a combination of patient history, physical examination, blood tests, and the exclusion of other diseases that share similar symptoms. The overall diagnostic process is aimed at building a strong clinical case supported by objective laboratory evidence of systemic inflammation.
Initial Clinical Assessment and Criteria
The diagnostic journey for PMR begins with a detailed assessment of the patient’s reported symptoms and a thorough physical examination. A strong clinical suspicion arises when a patient over 50 years old reports new-onset pain and stiffness that is symmetrical, meaning it affects both sides of the body. This discomfort is typically localized to the shoulder and pelvic girdles, often making simple movements like getting out of bed or raising an arm difficult.
A hallmark feature of PMR is morning stiffness that lasts longer than 45 minutes, often persisting for several hours. This prolonged stiffness is a key differentiator from non-inflammatory conditions. The physical exam may reveal a restricted active range of motion in the shoulders and hips due to pain, though the passive range of motion is often preserved. Patients may also report constitutional symptoms, such as fatigue, malaise, and a low-grade fever.
Interpreting Essential Inflammatory Markers
Once a clinical suspicion is established, blood tests are performed to look for objective signs of inflammation. The two primary laboratory markers used in PMR diagnosis are the Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP). Both tests measure generalized inflammation, which is a characteristic feature of PMR.
ESR and CRP Markers
The ESR measures how quickly red blood cells settle over an hour, with a faster rate indicating higher levels of inflammatory proteins. A value of 40 mm/hr or higher is often used as a threshold in diagnostic criteria. The CRP test measures a specific protein produced by the liver in response to inflammation and is often considered a more sensitive indicator of disease activity in PMR than the ESR.
Significantly high levels of both ESR and CRP strongly support a PMR diagnosis. However, these markers can be elevated in many other conditions, making them non-specific. In a small minority of PMR cases, the ESR and CRP may be normal, which complicates the diagnosis and requires greater reliance on clinical symptoms.
Differential Diagnosis and Exclusion of Similar Diseases
Because PMR symptoms and inflammatory markers are non-specific, diagnosis involves ruling out other diseases that mimic its presentation. This is why PMR is often called a diagnosis of exclusion. One of the most common look-alikes is Elderly-Onset Rheumatoid Arthritis (EORA), which can also cause pain in the shoulders and hips.
To differentiate EORA from PMR, doctors test for specific autoantibodies, such as Rheumatoid Factor (RF) and anti-Citrullinated Protein Antibodies (anti-CCP). The absence of these antibodies helps to exclude EORA, as their presence is characteristic of rheumatoid arthritis. Other conditions that must be considered and excluded include various infections, certain types of cancer, thyroid disorders, and other rheumatic diseases.
The most concerning condition to rule out is Giant Cell Arteritis (GCA), an inflammatory disease of the blood vessels that coexists in about 10% to 20% of PMR patients. GCA presents with symptoms like new-onset headache, jaw pain when chewing, and potential vision loss. Specialized tests like a temporal artery ultrasound or biopsy may be necessary if GCA is suspected, as this condition represents a medical emergency.
The Diagnostic Role of Steroid Response
The final piece of the diagnostic puzzle is the patient’s response to a therapeutic trial of low-dose glucocorticoids, or steroids. A dramatic and rapid improvement in symptoms following the start of steroid treatment is highly characteristic of PMR. Patients typically experience significant relief from pain and stiffness within 24 to 72 hours of taking the initial dose, often prednisone at 10 to 15 mg per day.
This swift resolution of symptoms serves as a practical confirmation of the PMR diagnosis. If the patient’s pain and stiffness do not improve quickly or substantially on a low dose of steroids, the PMR diagnosis must be reconsidered. A poor response suggests the patient may have an alternative condition, or potentially a more complex issue like GCA that requires a higher dose.