The diagnosis and classification of giant cell arteritis.

Giant-cell arteritis (GCA) involves the major branches of the aorta with predilection for the extracranial branches of the carotid artery. It occurs in individuals older than 50 years and the incidence increases with age. The signs and symptoms of giant cell arteritis can be classified into four subsets: cranial arteritis, extracranial arteritis, systemic symptoms and polymyalgia rheumatica. Patients may develop any combination of these manifestations, associated with laboratory evidence of an acute-phase reaction. The only test that confirms GCA diagnosis is a temporal artery biopsy, showing vasculitis with mononuclear cell inflammatory infiltrates, often with giant cells. Due to the focal and segmental nature of the infiltrates, areas of inflammation may be missed by the biopsy and the histological examination is normal in about 15% of the cases. Some imaging modalities may aid in the diagnosis of GCA. Among those, color duplex ultrasonography of the temporal arteries is more commonly used. There are no independent validating criteria to determine whether giant cell arteritis is present when a temporal artery biopsy is negative. The American College of Rheumatology criteria for the classification of giant cell arteritis may assist in the diagnosis. However, meeting classification criteria is not equivalent to making the diagnosis in individual patients, and the final diagnosis should be based on all clinical, laboratory, imaging and histological findings. Glucocorticoids are the treatment of choice for GCA. The initial dose is 40-60 mg/day for most uncomplicated cases. Addition of low-dose aspirin (100 mg/d) has been shown to significantly decrease the rate of vision loss and stroke during the course of the disease.