Epidemiology
Polymyalgia rheumatica (PMR, polymyalgia) is an inflammatory rheumatic disease that is often associated with giant cell arteritis (temporal arteritis). The disease occurs practically only in people over the age of 50 and has a relatively high prevalence of approx. 1% in this age group. However, there are clear regional differences in prevalence, such as a pronounced north-south divide.
Clinical presentation
The typical presentation suggestive of PMR would be a patient of advanced age (at least >50 years), with subacute to chronic pain and stiffness in the shoulder girdle, pelvic girdle, neck and trunk, typically occurring symmetrically. Patients often report difficulties with everyday activities, such as personal hygiene, putting on stockings, etc. There is often a pronounced feeling of illness with subfebrile temperatures, fatigue, loss of appetite and weight loss. High fever spikes are not typical and should always make one think of temporal arteritis, especially if the patient is even older (average age of temporal arteritis at onset: approx. 72 years; see below). It is also not uncommon for PMR to be accompanied by synovitic swelling of the peripheral joints, which often makes it difficult to differentiate from primary inflammatory joint diseases such as rheumatoid arthritis, or diffuse swelling ("pitting edema") of the soft tissues of the periphery of the extremities. However, the synovitis is spontaneous but quickly reversible, at least in response to steroid therapy.
Diagnosis of PMR
Typically, four criteria are used to establish the diagnosis of PMR:
- Age > 50 years: Age is the greatest risk factor for PMR. As with giant cell arteritis, there are practically no cases of patients under the age of 50.
- Bilateral pain and stiffness in the shoulder and pelvic girdle including upper arms and thighs, neck or trunk: muscle weakness is not typical for patients with PMR, but this can manifest itself in chronic forms if muscle atrophy is also present. In addition, synovitis is relatively common, sometimes accompanied by oedema of the hands or feet.
- Erythrocyte sedimentation rate (Westergren) > 40mm/h: lower values are also rarely found, but usually at least one of the acute phase markers is elevated, e.g. C-reactive protein or interleukin-6. In these cases, the marker that best detects the inflammation should also be included as a progression marker. Further laboratory tests are usually not helpful and the patients do not show a specific immunological serological profile, e.g. they are typically seronegative for rheumatoid factor, antinuclear antibodies and ANCA.
- Prompt response to steroid therapy: This criterion is not considered by many to be fully valid, but rapid improvement is often of differential diagnostic value in clinical practice.
Other imaging examinations, such as MRI of the joints, usually do not provide any additional exclusions
PMR and giant cell arteritis
Approximately 15% of patients with PMR also develop giant cell arteritis (GCA) over time. Conversely, 50% of patients diagnosed with GCA also have polymyalgia rheumatica.
GCA is a chronic vasculitis of the large and medium-sized vessels. The presentation of GCA is typically systemic and with potentially extensive vascular involvement. However, involvement of the cranial vascular branches arising from the aortic arch is the most common form of presentation.
GCA is characterised by headache, which is often localised, as well as pressure-painful and weakened pulsating temporal arteries, a high erythrocyte sedimentation rate (>50mm/h) in older patients (the disease practically never occurs before the age of 50; average age at diagnosis: 72 years). Histologically, there is typically a necrotising arteritis with a predominance of mononuclear cells or a granulomatous inflammation with the eponymous multinucleated giant cells. In patients with pure PMR without symptoms suggestive of GCA, a biopsy of the temporal arteries is usually crowned with relatively little success. On the other hand, the prevalence of subclinical inflammation of the large vessels is probably significantly higher than generally assumed. In most patients with PMR, examinations such as positron emission tomography (PET scan) therefore show an increased uptake of radiolabelled glucose in the area of the large vessels, but the clinical relevance of such findings is not entirely clear. It is possible that such patients could benefit from an even higher therapeutic dose of glucocorticoids.
In any case, the most feared complication of GCA is acute loss of visual acuity, often due to occlusion of the central retinal artery. In patients presenting with partial or total loss of vision, immediate intravenous therapy with high doses of methylprednisolone is indicated. In patients with GCA without visual impairment, the typical starting dose of prednisolone is 40-60mg daily.
PMR and malignancy
There is no association per se between pure PMR and malignancies. Nevertheless, polytopic myalgias and arthralgias in the context of paraneoplastic syndromes can often resemble PMR. Typically, such paraneoplastic pain differs from PMR by the lack of response to steroid therapy. This is often helpful in the differential diagnosis.
Furthermore, patients with multiple myeloma, who may present with bone pain and high prolapse, are not always easy to distinguish from PMR.
Therapy of PMR
Corticosteroids are the central therapy for PMR. Despite this fact, there are still no unanimous guidelines on the use of these drugs. However, relatively low doses, around 7.5-20mg, are usually sufficient to achieve significant symptom relief. However, the frequency of relapses is high, which is usually caused by reducing the steroid dose too quickly. In this respect, as a rule of thumb, a reduction of 10% of the dose every 2 weeks can be aimed for, and from a dose of 10mg then extremely carefully with reductions of no more than 1mg/month. The need to reduce cortisone must be weighed against the risk of renewed, higher-dose therapy if a flare-up occurs. After all, such relapses occur in 25-50% of patients. The same rule of thumb can be applied to giant cell arteritis, which is initially treated with higher doses.
Methotrexate is often used as basic immunosuppression with the aim of reducing the need for steroids over time. Unfortunately, the data regarding the benefit of methotrexate in both polymyalgia rheumatica and giant cell arteritis is controversial, and methotrexate is therefore indicated for very few patients with these conditions.
A frequently encountered problem is the assessment of disease activity over time. In the simplest case, this can be achieved by combining clinical symptoms and measurement of acute phase parameters. Here, not only the erythrocyte sedimentation rate is helpful, but it can also be replaced by the C-reactive protein if the erythrocyte sedimentation rate is not elevated in certain patients. Other acute phase markers, such as interleukin-6, can provide additional information.
Summary
Polymyalgia rheumatica is a benign rheumatic systemic disease that can usually be easily differentiated from myopathies of other origins due to its pronounced inflammatory activity. PMR has a self-limiting character by nature and does not show increased mortality. It shows an association with vasculitis of the larger vessels, the travelling cell arteritis. This can potentially have very serious consequences if incomplete or even complete loss of vision occurs due to eye involvement. The treatment of PMR and giant cell arteritis centres on corticosteroids, whereby particular attention must be paid to careful dose reduction in order to avoid relapses of the disease.
Prof. Dr. Daniel Aletaha