Is inflamed temporal arteries life threatening?

No but you could: Lose your vision if not treated immediately with steroid if you had temporal arteritis.

Sight threatening: Temporal arteritis (aka giant cell arteritis) is an inflammatory condition of large and medium-sized arteries, including the arteries feeding the eye. Symptoms include headache, jaw pain, visual disturbances and others. If not treated promptly with steroids it can lead to blindness in one or both eyes.

Possibly: Temporal arteritis or giant cell arteritis is an inflammatory condition involving the arteries in the head and scalp just in front of the ears. It is associated with anemia and inflammation that if untreated can lead to blindness, stroke and death. It is managed with steroids like Prednisone which must be taken typically for 6 months after an attack of temporal arteritis.

Yes it can.: Giant cell arteritis can lead to serious arterial blockage and death. However, older therapies used long courses of high dose steroids, which always have significant side-effects. Most current research suggest tnf-alpha inhibitors, used immediately can work better than steroids, and certainly lower the dose of corticosteroid if needed. Google it!