For olde tyme fun, Gout and Scurvy lead the pack, IMHO.
but through all the latin of modern diagnosis, the best disease name ever is a recent one: Monkey Pox!
My aunt recently had a bout of Cradle Cap (a fungal infection of the scalp usually seen in infants but also seen in bed bound elders).
Aside: She went through many courses of standard medical treatment but could not get rid of this fungus. A gal who occasionally comes to take care of her said on old time remedy was to slather the scalp in Vicks vaporub. Believe it or not, that worked (but it was a real pain to wash out of her hair).
What, no brain fever?
I think brain fever is one of my all-time favorites. I remember it from a number of Sherlock Holmes stories. Someone discovers something horrible, and they immediately faint and are carried to bed, to languish there for months with brain fever.
“FLK” is shorthand for “Funny Looking Kid”, which could indicate any one of a number of developmental disorders, or just that the kid is ugly. My sister, a PT, says she’ll still sometimes see this in patient’s charts, though its use is strongly discouraged.
We used to amuse ourselves with “The Ugly Baby Book” I think the real name was Congenital Anomilies
Syphalisis is always fun
Abraham Lincoln’s mother, aunt and uncle died of “the milk sick”, which is caused by drinking milk from a cow that has eaten white snakeroot. This was also known as “puke fever”
As a humorous music dictionary said, this is the disease supposed to afflict operatic sopranos in the role of Mimi in La Bohème; the audience is asked to accept that a 200-pound woman who sings for four hours is wasting away.
I’m told that the same disease can afflict teachers, due to excessive exposure to chalk.
Another horrible cause of it is sexual violence, to the point that fistulas become a severe problem in areas where rape is used as a weapon of war. I remember reading an interview with a beleaguered gynecological surgeon working in Africa for very little money, trying to treat as many brutalized women and girls for fistula as he could.
An epizootic is an epidemic among animals – zoon (animal) instead of demos (people).
I remember reading that at one particular period (the thirties?) there was a severe epizootic in some area of the United States, and the word was bandied about enough that “the epazutics” or some similar phonetic alteration came to mean “some unspecified ailment” (or as my grandfather would say, “diaplupus of the plux”).
Is Zombieism a disease?
I had shingles, which is a recurrence of the 'pox, which lives in your body forever. Nowadays though it had a boring name: herpes zoster. It really sucks to have a disease called “herpes,” even though it’s the same virus that causes chicken pox.
Small nitpick; scarlet fever is a variant of strep that occurs with or without treatment, not a complication of untreated diease and it is still very much around.
I personally like the spirochetal diseases (Yaws, Pinta and Syphilis-although for some reason I always want to call them Yaws, Pinta and Santa Maria).
Hansen’s Disease (Leprosy) is also good.
My favorite recent diagnosis was a patient with Dysphagia Lusoria-which nobody I know had ever heard of.
What, no piles yet? Which are hemorrhoids. I don’t think they are a disease so much as a state of being.
A clyster will cure many of these maladies.
Interesting accounts of ‘The consumption’ and conjunctivitis are given in Frank McCourt’s “Angela’s Ashes.”
Depends on which movie you watch, although it’s not an old timey one either way.
Unless you go back to Haiti and voodoo. 
I thought of a couple more (although I’ve never had them):
Lycanthropy (Hypertrichosis)
Vampirism (Porphyria)
Demon Possession (Epilepsy or dissociative identity disorder)
I’m not sure if they’re medical conditions back in the day, but apparently Demon Possession is a recognized psychiatric condition in the DSM-IV.
Does anybody get catarrh anymore?
The best cause of death I’ve seen so far is in one of our 19th century parish books, where the minister had dutifully noted Alcoholismus chronicus. These days it would probably be archived as acute liver failure or something similar.