Giant cell arteritis can occur as local vascular disease or as part of a systemic illness that includes fever, malaise, weight loss and/or polymyalgia rheumatica. Definitive diagnosis of giant cell arteritis requires a positive temporal artery biopsy, although false-negative results can occur because of the patchy distribution of lesions. Polymyalgia rheumatica is a syndrome affecting elderly patients and is characterized by proximal pain and stiffness of the shoulder, neck or pelvis. About one half of patients with giant cell arteritis have polymyalgia rheumatica, and from 10 to 15 percent of patients with polymyalgia rheumatica without local evidence of vasculitis have giant cell arteritis on biopsy. There are also shared immunologic abnormalities.

The distinction between these diseases is important because polymyalgia rheumatica is treated with low-dose corticosteroid therapy, whereas giant cell arteritis requires high doses of corticosteroids. Rodriguez-Valverde and colleagues conducted a retrospective study to identify predictors of a positive temporal artery biopsy and to define a predictive model for either a high or low probability of giant cell arteritis in patients with polymyalgia rheumatica.

Patients were defined as having polymyalgia rheumatica if they met the following criteria: age 50 years or greater at the onset of disease; erythrocyte sedimentation rate greater than 40 mm per hour (Westergren); bilateral moderate or severe pain involving at least two of the following areas: neck, shoulder and pelvic girdles; and rapid resolution of the syndrome (in less than seven days) with low-dose prednisone (5 mg twice daily in most cases).

Risk for an abnormal arterial biopsy was increased in patients who were 70 years of age or older at disease onset, had a new headache or abnormal temporal arteries on physical examination, and had jaw claudication. Raised liver enzymes also significantly increased the likelihood of a positive temporal artery biopsy.

The authors conclude that giant cell arteritis is especially likely in patients with polymyalgia rheumatica who are older than 70 years of age and who have a new headache, jaw claudication, raised liver enzymes and evidence of abnormal temporal arteries on physical examination. Because of the significant side effects of high-dose corticosteroid therapy, confirmation by temporal artery biopsy is still recommended in the elderly population to make a definitive diagnosis. Patients without these high-risk factors can be safely treated with low-dose corticosteroids without biopsy.