Relationship with polymyalgia rheumatica

A close relationship exists between GCA and polymyalgia rheumatica (PMR). Despite numerous reports associating these 2 disease entities, the precise nature for this association is poorly understood and currently unknown. However, it is evident that both conditions affect similar patient populations and frequently affect the same individual. Several authors have suggested that these 2 diseases are actually different stages of a single disease spectrum. See Special Concerns.

Pathophysiology: GCA typically involves inflammation of the aortic arch and its branches, but almost any artery of the body as well as some veins may be affected occasionally. The inflammation tends to involve the arteries in a segmental or patchy manner, although long portions of arteries may be involved. The likely determinant of arterial susceptibility to GCA is the presence and/or quantity of internal elastic lamina within the vessel wall. For example, intracranial cerebral vasculature is not affected in GCA because these vessels lack an internal elastic lamina.

The extracranial vertebral arteries, superficial temporal arteries, posterior ciliary arteries, and ophthalmic arteries are the most commonly involved arteries. The internal carotid, external carotid, and central retinal arteries are affected somewhat less frequently. In some postmortem studies, lesions were found in the proximal and distal aorta, subclavian, brachial, and abdominal arteries. Intracranial arteries are involved infrequently.

Histopathology (see Histologic Findings) in GCA reveals inflammatory infiltrate surrounding a fragmented internal elastic lamina within the media of an arterial wall. The infiltrate consists predominantly of mononuclear cells with giant cell formation. The mechanism is believed to be related to dysfunction of cellular immunity, but the etiology is unknown (see Causes for more information).

Frequency:
 

• In the US: The reported incidence of GCA varies from approximately 0.5-27 cases per 100,000 people aged 50 years or older. The annual incidence is higher in northern areas of the US.

  In Olmstead County, Minnesota, 125 cases were identified over a 42-year review representing an average annual incidence rate of 17.8 cases per 100,000 population aged 50 years and older and a prevalence of persons with active or remitted GCA of 200 cases per 100,000 population aged 50 years or older. A regular cyclical pattern in incidence over 20 years has been noted.

• Internationally: The annual incidence in northern European countries has been reported to be more than 20 cases per 100,000 people. Scandinavian countries have reported the highest incidence.

  The annual incidence in southern European countries has been reported to be less than 12 cases per 100,000 people. In Lugo, Spain, the average annual incidence for the population aged 50 and older was 10 cases per 100,000 people.

  Ostberg reported that autopsy studies performed on 889 postmortem cases revealed arteritis (temporal artery, aorta) in 1.6% suggesting that GCA may be more common than is clinically apparent.

  The incidence of GCA in Saudi Arabia is probably less than in the US and Western Europe. In 1998, Bosley and Riley reported only 4 positive biopsy results from 72 temporal artery biopsies performed over a 15-year period.

Mortality/Morbidity: In the milder form of GCA, patients may complain only of generalized muscle aches and pains and unusual fatigue. These may be mistaken for symptoms of polymyalgia rheumatica. Intermittent claudication occurs in about 50% of patients. During chewing of firm foods such as meat, fatigue or discomfort of the jaw muscles is noted. In a small percentage of patients, claudication of the tongue or throat develops with eating and repeated swallowing. Nervous system alterations are found in as many as 30% of patients; 14% have either mononeuritis or polyneuropathy, and 7% have transient ischemic attacks or strokes.

• Visual symptoms are present in about 33% of patients; 40-50% are transient (amaurosis fugax and diplopia) and 50-60% are permanent. Regarded as one of the more serious complications of GCA is the onset of blindness from involvement of the ophthalmic artery. Permanent visual loss may be partial or complete and may occur without warning; about 50% are unilateral and 50% are bilateral. Varied visual symptoms including blurring of vision, diplopia, and loss of vision occur in 36-60% of patients.
  
   

• Rarely, the inflammatory process may weaken the aortic wall, leading to localized aneurysm formation, aortic annular dilatation, and aortic regurgitation. Narrowing or occlusion of the branch vessels of the thoracic aorta (clinically referred to as aortic arch syndrome) may be found in 9-14% of cases, producing symptoms similar to those of Takayasu arteritis (decreased upper extremity pulses and blood pressure, arm or leg claudication, Raynaud phenomenon, transient ischemic attacks, coronary ischemia, and abdominal angina).

• Aortic aneurysms, aortic regurgitation, and aortic dissection occur less commonly. Evans and colleagues reported aortic aneurysms occurring in 15% of patients at a median of 6 years after the GCA initially was diagnosed. Two thirds were thoracic aortic aneurysms, with the majority located in the ascending aorta. Almost 33% developed symptomatic aortic regurgitation.

• Involvement of major vessels (aorta) predisposes patients to higher risks for death. In Evans and colleagues' report, 50% of those with thoracic aortic aneurysms died suddenly from aortic dissection.

Race: Incidence rates appear to be higher in Caucasians of European descent. This condition is less common in African Americans and Asians.

Sex: Women are 2-4 times more likely to have GCA than men.

Age: Age is the most important risk factor for GCA.

• GCA occurs mostly in patients older than 50 years, with incidence increasing with age and peaking in the eighth decade. The disease is rare in patients younger than 50 years.

• Although the increasing incidence of GCA after age 50 years implies a relationship to aging, the meaning of this observation is not fully understood.