I have a death certificate for a woman who died at the age of 42. The cause of death is listed as "disease of the brain". I am not sure what that could mean. Did they mean meningitis or some type of infection or do they mean that she had a mental issue. Would mental instability be referred to as a disease? I am particularly intrigued because the poor woman lost two young infant due to "accidental suffocation". The coroner's verdict was accidental death. The deaths occurred in Liverpool, England in the early 1870's.
It is unlikely to be meningitis as that disease was known to medicine well before that time.
It is the case that many forms of mental illness were described just as a disease of the brain in the late 1800s. The accidental suffocation could conceivably be related as you suggest.
I have a similar circumstance in my ancestry. A woman tried for murder of her baby who was found not guilty by reason of insanity. She was committed for life to an asylum. The trial transcript shows that doctors stated she had a disease of the brain. I believe we would now call this Post-natal Depression. How things have changed...