POLYMYALGIA RHEUMATICA

Polymyalgia rheumatica is characterized by proximal symmetric limb girdle pain and stiffness that may be accompanied by systemic inflammatory features. The disease responds in dramatic fashion to low-dose corticosteroids. The lack of response to corticosteroids raises the possibility of an alternative diagnosis.

Epidemiology. Polymyalgia rheumatica is extremely uncommon in persons younger than 50 years old. Mean age at onset is 73; women are affected three times more often than men. Whites of northern European or Icelandic descent have a higher incidence of the disease than other ethnic groups.

Pathophysiology. The etiology of polymyalgia rheumatica and giant cell arteritis is unknown. Aging produces dramatic changes in immune, as well as, tissue substrate (e.g., vascular and other tissues). Although such changes are universal in aging, giant cell arteritis and polymyalgia rheumatica remain relatively uncommon, suggesting that additional factors, beyond aging, are at play.

What is the argument for polymyalgia rheumatica being a mild form of giant cell arteritis? The patient demographics for both diseases are identical, and giant cell arteritis is commonly associated with polymyalgia rheumatica. In both diseases, two thirds of patients have the HLA-DRB1*04 allele, and, apart from INF-γ, have similar mRNA for cytokines in temporal artery biopsies. This suggests that in polymyalgia rheumatica there are small but significant numbers of type 1 T-helper (Th1) lymphocytes within the vessel wall but that IFN-γ may be necessary to enhance that response so that it appears as vasculitis.

Clinical Manifestations. Most patients have subacute onset of symptoms. Seventy to 95 percent report neck and symmetric shoulder girdle pain and morning stiffness. Fifty to 70 percent report hip girdle pain and stiffness. Fever, malaise, anorexia, or weight loss may occur in about one third of patients.

Diagnosis. The diagnosis of polymyalgia rheumatica is primarily clinical. The ESR is greater than 40 mm/hr in 90% of cases. Limb girdle pain, morning stiffness, elevated ESR, and a rapid response to low-dose corticosteroids are compatible with this disease. Elevated CRP, normocytic normochromic anemia, thrombocytosis, and elevated alkaline phosphatase may also be present. Muscle enzyme levels are normal.

Conditions that can mimic polymyalgia rheumatica include malignancies, myositis, and proximal-onset rheumatoid arthritis.

Treatment/Prognosis. Corticosteroids are the only consistently effective intervention. Prednisone or prednisolone is usually started in doses of 15 to 20 mg/day. A dramatic response, with near-total relief, should occur within days. After improvement is sustained for 2 weeks to 1 month, a slow taper should begin. The goal is to achieve the lowest effective dose that provides a symptom-free state. Disease flares with corticosteroid tapering are common and often require temporary increase in therapy. Adverse events from corticosteroids occur in almost every patient. The role of immunosuppressive agents other than corticosteroids is of doubtful utility.

Careful follow-up to assess possible drug-related toxicities and expression of the features of giant cell arteritis is essential. New-onset atypical headache, visual changes, murmur of aortic insufficiency, or features of large vessel ischemia should lead to immediate evaluation and institution of higher doses of corticosteroids. Bilateral upper and lower extremity blood pressures should be obtained periodically. Differences between contralateral extremity pressures of more than 10 mm Hg may be an indication of subclavian, iliac, or femoral artery involvement. The finding of bruits over large vessels may be due to atherosclerosis and/or giant cell arteritis and will require vascular imaging evaluation.

GIANT CELL ARTERITIS

GCA is due to a granulomatous inflammatory injury to medium-sized and large arteries. The most frequently affected vessels are the extracranial branches of carotid arteries and other primary branch vessels of the aortic arch. Less often, internal branches of the carotid are affected, most notably the ophthalmic and posterior ciliary arteries, which when stenotic or occluded may cause visual ischemia or blindness. An exhaustive postmortem study demonstrated that all patients have large vessel inflammation. However, clinically apparent large vessel sequelae occur in only about 25% of cases. This is most often the result of stenoses (especially of the subclavian artery) or aneurysms of the aorta (with the thoracic aortic root affected much more often than the abdominal aorta) or its branch vessels.