Beth Uffner, an avid tennis player, developed an aching pain first in her legs, then in her shoulders that got progressively worse until she lacked the strength to get out of a chair unaided, let alone play tennis. Faith Sullivan, a novelist, developed a headache so devastating that she could hardly read and had to take a fistful of aspirin to get through a scheduled talk about her books.

Both women were in their mid-70s when they were seized by different but related inflammatory autoimmune conditions — polymyalgia rheumatica in Ms. Uffner, temporal arteritis in Ms. Sullivan. Both disorders can sometimes afflict the same person. And while both are life-inhibiting, giant-cell arteritis, as temporal arteritis is also called, is especially dangerous. A delay in treating the cause of this viselike head pain can result in irreversible vision loss, a stroke or even death.

Prompt and proper treatment with a corticosteroid like prednisone can quickly relieve symptoms of both conditions. But the therapy must be carefully managed by a knowledgeable physician — in most cases, a rheumatologist — to minimize side effects and produce a lasting remission.

As I learned from speaking with both women, it is important for people with symptoms suggestive of these disorders to resist the tendency to assume they’re nothing serious — that they will soon resolve on their own with an over-the-counter remedy to counter the pain. As a septuagenarian athlete, Ms. Uffner, a New Yorker, was used to having aches and pains. She self-treated with lots of ibuprofen for several months until this nonprescription remedy was no longer enough to get her through a normal day.