Dear Annie: A few years ago, my husband — always kind, patient and gentle throughout our nearly 40-year marriage — began behaving in ways that shocked me. He became verbally cruel, aggressive, and would erupt in sudden fits of rage over seemingly nothing. It escalated to the point where he threw a plastic water bottle at me and threatened to hit me — something entirely out of character. I took it seriously, had him arrested and pushed for a medical evaluation when he refused to seek help on his own.

To everyone’s surprise, tests revealed he had suffered a small stroke — specifically in the part of the brain that governs personality and emotional regulation. He had none of the typical symptoms like slurred speech or loss of motor skills, only this frightening and drastic personality change. With treatment and medication, he’s improved significantly, and while some anger still surfaces, we understand the root cause now.

I often read letters from people whose spouses are struggling with unexplained behavioral changes later in life, and I wonder: How many of these cases could be due to a silent medical issue such as a stroke or neurological condition?

When a longtime partner suddenly changes in disturbing or aggressive ways, how can a spouse distinguish between emotional issues, mental illness and an underlying medical condition such as a stroke? What steps should one take to get help, and how do you balance love and safety during such a crisis? — Still Together After 40 Years

Dear Still Together after 40 years: Thank you for bringing more awareness into the possibilities of personality changes later in life. Taking your husband’s threat seriously and insisting on a medical evaluation saved your marriage.

Many people don’t realize that strokes or neurological issues can cause sudden, drastic changes in personality without the classic physical symptoms. Your experience is a vital reminder that behavioral changes, especially sudden aggression or confusion, can have medical causes.

I hope your letter brings awareness and hope to others in similar situations.

Read more Dear Annie and other advice columns.

“How Can I Forgive My Cheating Partner?” is out now! Annie Lane’s second anthology — featuring favorite columns on marriage, infidelity, communication and reconciliation — is available as a paperback and e-book. Visit Creators Publishing for more information. Send your questions for Annie Lane to [email protected].