What to Know About Post-Shingles Encephalitis

Dianne Feinstein, a Democratic senator from California, has returned to the Capitol after spending more than two months recovering from shingles. The disease, often characterized by a painful rash, is triggered by the same virus that causes chickenpox, which stays in people’s bodies for life and, years later, can become reactivated.

For Ms. Feinstein, 89, the virus also brought on a previously unreported case of encephalitis, a rare but potentially debilitating complication in which the brain swells. The condition is often caused by an infection or an immune response.

What are the symptoms of encephalitis?

Post-shingles encephalitis can cause headache, fever, sensitivity to light, vomiting, confusion, a stiff neck or even seizures.

It can also leave some patients with more lasting problems. Those include memory or language trouble, sleep disorders, mood disorders, walking difficulty and other cognitive problems. Older patients tend to have the most trouble recovering.

There are milder and more serious cases. A French study from last year looking at several dozen critically ill patients with the condition found that about one-fifth of them were significantly disabled a year after being hospitalized and one-third had died.

A separate study in Denmark from 2020 found that roughly half of post-shingles encephalitis patients admitted to hospitals were at least moderately disabled three months after being discharged.

How common is the condition?

Dr. Adrien Mirouse, a physician and immunologist based at Sorbonne University in Paris, who led the French study last year, estimated that fewer than 1 percent of shingles patients go on to develop encephalitis.

But precise rates, he said, were difficult to pin down: Milder cases often go unreported, making it hard to know the real number of patients with shingles or post-shingles encephalitis.

Brain swelling has historically been thought to affect mostly those shingles patients with immune deficiencies. But recent studies have found that many patients are simply older and struggling with a routine weakening of their immune systems. For that reason, the condition may be increasingly common as populations age, experts said.

What is the outlook for patients?

It is not entirely clear why some shingles patients who develop encephalitis fare better or worse with the condition. Older age appears to put people at greater risk for more serious problems.

But published case studies have described even younger patients who show signs of retrieving their cognitive functions, only to deteriorate again.

“You may have some symptoms that last after the encephalitis,” Dr. Mirouse said of patients. “It’s not sure you will be able to recover completely. That’s true at 89, it’s also true at 30 or 20.”

Ms. Feinstein may have been at higher risk for developing encephalitis because her shingles had spread to her face and neck, which is known to put patients at risk of brain inflammation.

How else can shingles affect people’s cognition?

Inflammation alone can damage cells in the brain.

But shingles can also contribute to cognitive decline in other ways, including by damaging blood vessels of the brain, said Dr. Sharon E. Curhan, a physician and epidemiologist at Brigham and Women’s Hospital and Harvard Medical School, who is studying the link between shingles and changes in cognition.

Shingles patients also face a significantly higher long-term risk of having a stroke, a condition that itself can lead to cognitive decline, according to a study led by Dr. Curhan published last year.

Ms. Feinstein had received a shingles vaccine, which in most people provides strong protection against the virus and the complications that can follow. Federal health officials recommend the vaccine for people 50 and older and younger adults with weakened immune systems.