Encephalitis is an interesting thought as in 1991, my daughter in law ended up in intensive care at about 8 days post natal with encephalitis and it was only because the drug Zovirax had recently become available as an intravenous drug, that she survived. D.I.L is really skinny, but her face and head were so swollen that she was unrecognizable.
If it was encephalitis, and she swelled up like my D.I.L. then I guess they would call it softening of the brain. Otherwise - how would they have known? Did they do post mortems in 1881?
Stan - I doubt she had advanced syphilis at 21, especially as her husband was only 23 at the time himself. Not only that, when he died 5 years later he died of Phthisis with no mention of Syphilis. Also her father didn't die until 1904, so not a hereditary thing