Polymyalgia rheumatica (PMR) is an inflammatory rheumatic disease characterized clinically by pain and morning stiffness in the shoulders, waist, hip and neck. It may be associated with another disease, giant cell arteritis (GCA), and the two disorders may represent different manifestations of a common disease process.
PMR is two to three times more common than GCA. PMR occurs in approximately 50% of patients with GCA, while approximately 15% to 30% of patients with PMR eventually develop GCA. Some patients present with manifestations of both disorders at different times.
This disease is almost exclusively a disease of adults over 50 years of age, with a prevalence that increases progressively with age, affecting about 700 per 100,000 people in this age group, although the average age at diagnosis is over 70 years. In addition, women are affected two to three times more often than men.
Causes of polymyalgia rheumatica
The cause of PMR is unknown, but environmental and genetic factors appear to play a role. In addition to the frequent clinical association between PMR and ACG, there is also evidence of a pathogenetic similarity between the two disorders. In some cases, a cyclic pattern in incidence is shown, suggesting an environmental infectious trigger, such as Parvovirus B19, Mycoplasma pneumoniae and Chlamydia pneumoniae.
Symptoms of polymyalgia rheumatica
The most characteristic feature of the presentation of polymyalgia rheumatica is bilateral shoulder pain and stiffness of acute or subacute onset. Patients often also have concomitant pain and stiffness in the waist, hip, neck musculature. Muscle weakness is not a feature of the disease, although this may be difficult to assess in the presence of muscle pain; when symptoms are prolonged, disuse muscle atrophy may occur.
Stiffness after periods of rest and morning stiffness of more than one hour is also typical. Stiffness may be so profound that patients have great difficulty turning in bed, getting out of bed or out of a chair, or raising their arms above shoulder height (e.g., to comb their hair). Mild synovitis (inflammation of the tissue lining the inside of the joint capsule) may occur in the wrists and knees, and rarely in the feet and ankles. Especially early in the course of the disease, most patients present with systemic symptoms such as fatigue, loss of appetite, weight loss, low-grade fever, and sometimes depression.
Diagnosis of polymyalgia rheumatica
Diagnosis is based mainly on the clinical features described, in people over 50 years of age, who present with a duration of symptoms of more than two weeks. The rheumatology physician should perform basic laboratory tests, such as inflammatory markers (erythrocyte sedimentation rate and C-reactive protein), biochemical tests, hemogram (number of various types of cells in a given amount of blood) or urinalysis.
It is also important to perform imaging tests, including X-rays of the inflamed joints, magnetic resonance imaging, ultrasound, scintigraphy or positron emission tomography (PET-CT). The latter is the best method to thoroughly evaluate the inflammation of PMR and to rule out other diseases, such as rheumatoid arthritis, or occult neoplasms.
Treatment of polymyalgia rheumatica
Glucocorticoids are the only known effective treatment. The initial goal of treatment is to rapidly achieve symptomatic control with a relatively low dose of glucocorticoids. After a period of disease inactivity, the dose of glucocorticoids should be slowly tapered. Glucocorticosteroid treatment can often last two to three years, although 10% of patients will relapse within 10 years of progression and require longer treatments. The recommended dose of glucocorticoids is the lowest possible dose that will keep symptoms relieved.
It is also important to prevent and monitor side effects of glucocorticoids, such as osteoporosis, glucose intolerance and hypertension. If the required maintenance dose of glucocorticoids is high, a glucocorticoid-sparing agent should be added to decrease the possibility of glucocorticoid side effects.
In most patients, PMR has a self-limited course over months to years. However, some patients require long-term treatment and about 10% of patients relapse within 10 years after completion of their initial course of treatment. On the other hand, there is no evidence of increased mortality associated with PMR itself. Thus, all efforts should be made to control symptoms with minimal side effects from glucocorticoids.