At a Glance
Vasculitis is an inflammation of the blood vessel wall. The various systemic vasculitides are often categorized based on the size of the involved blood vessels, namely small-, medium-, and large-sized vessels. Giant cell arteritis (GCA) and Takayasu arteritis (TA) are referred to as large vessel vasculitides. In addition to the immune activation within the vessel wall, both disorders are characterized by a significant systemic inflammatory response. The specific clinical features associated with GCA and TA depend, in large part, on what specific arteries are affected with vasculitis.
Clinical Manifestations
Systemic features of inflammation, including significant weight loss, fatigue, and fever, are often present in patients with GCA, regardless of which specific arteries are involved. The classic features of GCA are headache, scalp tenderness, and jaw claudication. These symptoms are generally present in 50-80% of patients with GCA and result from inflammation of the neck and head arteries, often in branches of the external carotid artery.
Patients with external carotid artery vasculitis are at significant risk of visual disturbances and loss of sight if the inflammation is not treated quickly. In patients without involvement of the carotid artery, clinical symptoms are more nonspecific. In these patients, the most commonly affected arteries are the upper-extremity vessels and the aorta. The clinical symptoms associated with aortic inflammation include asymmetric blood pressure readings and asymmetric or absent pulses in the upper extremities. In a patient 50 years of age or older, any combination of these symptoms along with objective evidence of systemic inflammation should induce a diagnostic evaluation for GCA.
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The clinical features of Takayasu arteritis (TA) are similar to giant cell arteritis (GCA), especially compared to patients with GCA who lack temporal artery involvement. Systemic manifestations, including weight loss, fatigue, night sweats, and arthralgias, are common and are often the presenting clinical feature. The most commonly affected portion of the vasculature is the subclavian artery. Involvement of this artery can manifest as arm claudication and/or absent/decreased pulses.
In a smaller number of patients, the common carotid artery is involved, leading to visual disturbances and transient ischemic attacks. In some patients, the abominal aorta may have a significant inflammatory response, which could lead to abdominal angina. The age at which symptoms initially manifest can help distinguish TA from GCA. TA may be considered in a patient 40 years of age or younger with any of the previously listed symptoms accompanied by objective evidence of systemic inflammation.
What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?
Unfortunately, there are no laboratory tests specifically diagnostic for either GCA or TA. Instead, because both diseases are accompanied by a significant systemic inflammatory response, nonspecific markers of an acute phase reaction are often useful when there is a clinical suspicion of either large-vessel vaculitide. The most commonly ordered tests are the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). In addition, other potential markers of active inflammation may also be useful, such as fibrinogen, serum amyloid A, and the cytokine interleukin-6. Other nonspecific laboratory findings, such as thrombocytosis and anemia, may be present.(Table 1)
Table 1
| ESR | C-reactive protein |
|---|---|
| Elevated, generally >50 mm/hr | Elevated |
| Although not specific for GCA or TA, an abnormal response indicates an acute-phase reaction and a proinflammatory response. | Although not specific for GCA or TA, an abnormal response indicates an acute-phase reaction and a proinflammatory response. |
Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications – OTC drugs or Herbals – that might affect the lab results?
The treatment for GCA and TA is immunosuppression, with corticosteroids being the most commonly-prescribed medication. Unfortunately, patients who present with GCA or TA may be started on an immunosuppressive regimen, based on evidence of a chronic inflammatory process, before a specific diagnosis is established. For these patients, laboratory testing for acute phase reactants may not be informative, as the steroid or other immunosuppressive agent may result in decreased or possibly normalized ESR and CRP. Extreme caution must be used when interpreting a normal ESR or CRP in a patient being treated with corticosteroids (prednisone), methotrexate, mycophenolate mofetil, or biologic cytokine blocking agents, such as antitumor necrosis factor antibodies.
What Lab Results Are Absolutely Confirmatory?
Diagnosis of GCA can be confirmed by biopsy. In most cases, the site of choice for the biopsy is the superficial temporal artery. On histology, characteristic findings in GCA include a significant mononuclear cell infiltrate composed primarily of T cells and macrophages. Occasionally, multinucleated giant cells may be observed. Granulomas may also be present.
For TA, there is no testing, neither laboratory nor pathology, that can absolutely confirm the diagnosis. Instead, the diagnosis relies on clinical presentation, increase in nonspecific inflammatory markers, and imaging.
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