GCA is an autoimmune disease in which the body's immune system mistakenly attacks the person's own tissue. Autoimmune diseases in general are poorly understood. They tend to run in families, but not so much that we can say they're inherited or genetic diseases. Many doctors believe it takes a combination of predisposing genes and environmental factors to trigger the condition.

Early symptoms of GCA include fever, weakness, sweating, and weight loss, which may come on suddenly. These symptoms may go on to the classic symptoms of GCA, such as:

• double vision or blurred vision, or a black curtain coming over vision; these symptoms are due to narrowing of the main artery to the eye
• headache in the temple or back of the head (60% of people have this symptom)
• sensitive, tender scalp
• swollen, bumpy, tender arteries in the temple, often lacking a noticeable pulse
• weakness or pain in the jaw muscles or tongue – lack of oxygen to jaw muscles causes chewing brings on pain that goes away when stopped
• weight loss
• fever
• anemia and other blood abnormalities
• fatigue

If arteritis is left untreated, it can progress to the following symptoms:

• blind spots or sudden blindness in one eye
• stroke
• heart attack
• other serious conditions due to impaired blood flow in the arteries

Blindness is a serious threat in arteritis. In a few cases, vision loss is the first sign of GCA. Unfortunately, any damage already done is usually irreversible. Most people get warning symptoms (called prodromes), such as fluctuating vision, black curtains that briefly descend over vision in one eye (called amaurosis fugax), and headaches, giving them time to take action and see their doctor.

At least 50 % of GCA patients also have polymyalgia rheumatica (PMR). About 10% to 20% of people with PMR go on to develop GCA. Arteritis may appear before, during, or after the onset of PMR. The primary symptoms of PMR are severe stiffness and pain in the neck, shoulder, and hip muscles. There may also be fatigue, joint pain, and anemia.

GCA is diagnosed by a thorough physical examination, blood tests, and sometimes by taking a biopsy (tissue sample) of the affected temporal arteries. Two tests, the erythrocyte sedimentation rate (ESR) and C-reactive protein, are usually elevated in GCA. The ESR measures how fast erythrocytes (red blood cells) settle to the bottom of a thin test tube.

It may be necessary to do tests that take images of the blood vessels in the chest and neck and to check for signs of  damage. GCA can damage the aorta (the largest artery in the body, which originates in the heart) and other major vessels. Tests such as ultrasound, MRA and PET scans of the temporal artery can take images in a non-invasive manner. Sometimes, an angiogram needs to be done.

Despite the availability of non-invasive imaging, a biopsy is frequently needed for a diagnosis. This will involve taking at least an inch of vessel from one or both sides. In some cases taking bilateral (both sides) biopsies  can give a more reliable diagnosis.

Note that arteritis is an inflammation of the arteries that comes on over a fairly short period of time, which is different from atherosclerosis, which is hardening of the arteries that occurs gradually.

Giant cell arteritis (GCA) is treatable, and complications can be avoided when treatment is started early enough. As blindness and other severe consequences can come on suddenly, doctors will start treatment as soon as the disease is suspected; confirmation of diagnosis can be done after starting treatment.

The medication usually used is prednisone*, a corticosteroid that reduces inflammation. Treatment begins with a high dose to bring down the inflammation in the arteries under control. This is then slowly tapered to a lower dose that is called the "maintenance dose," as recommended by the doctor. A person who has vision problems will often be given methylprednisolone intravenously to start. Long-term use of corticosteroids poses a risk of serious side effects, and maintaining the lowest dose possible helps reduce those risks.

Some people need to keep taking low doses for a year or two before their doctor can be sure that symptoms won't return. Others may need to take prednisone for 5 to 10 years or indefinitely. Sometimes, symptoms recur a few times early in treatment and the dosage has to be temporarily raised. GCA usually does not recur after treatment is finally stopped, but a person with aortic disease needs to be monitored regularly by their doctor once it occurs.

The following side effects are associated with corticosteroid use, but they are much less likely with the lower doses given for GCA after gradually tapering from the initial high dose to a lower dose:

• degeneration of hip or shoulder bones
• diabetes
• easy bruising
• fluid retention and weight gain
• glaucoma
• higher blood pressure
• increased susceptibility to infections, including serious infections
• osteoporosis (your doctor may recommend taking calcium and vitamin D supplements to help prevent osteoporosis)
• reactivation of hidden tuberculosis or other chronic infections - people who test positive for tuberculosis need to take tuberculosis-preventive medication
• rounding of the facial features
• slower healing of wounds
• stomach irritation
• muscle weakness (sometimes permanent)

Prednisone is also used to treat polymyalgia rheumatica, but at a much lower dose. Symptoms are usually eliminated within a day or two or up to one week after the first dose. The dose is then slowly reduced and maintained at lower doses for at least several years and sometimes longer.

The medication tocilizumab may be given with oral steroids, or by itself after a steroid regimen has been completed. Other immunosuppressant medications, such as azathioprine, methotrexate, or biologics have not been clearly shown to be helpful, though some experts feel they may have some value.

Doctors may also prescribe low-dose (81 mg daily) acetylsalicylic acid (ASA) to help lower the risk of blindness or stroke. These complications may result if the blood flow carrying oxygen to the optic nerve or to the brain is cut off due to the arteritis.

There's no easy way to prevent arteritis, but a healthy lifestyle and not smoking are always important.

Above all, see a doctor if you have the symptoms listed in the "Symptoms and Complications" section. As many as 1 in 5 people with this disease will go blind without treatment, but prompt treatment can make a big difference. Not all physicians recognize the early clues. Rheumatology is the field with most expert experience in GCA and PMR. You should also get your eyesight checked every 2 years if you're over 50 years of age, and every year if you have diabetes.