This evidence suggests that Beethoven died of complications resulting from
renal papillary necrosis, more commonly known as
kidney failure. A common cause of papillary necrosis is
diabetes, but Beethoven did not suffer from that condition to our knowledge. Other common causes include
hypertension or
analgesic nephropathy, which is essentially a fancy term for abusive overuse of painkillers. Beethoven also clearly had severe
cirrhosis of the
liver, a condition which is
comorbid with papillary necrosis (the cirrhosis was likely due to Beethoven's known alcohol abuse, and possibly also
hepatitis).
Beethoven was known to suffer from a variety of aches and pains late in his life, and seems to have had a fondness for painkillers. One of the commonly used painkillers at the time was salicin (dried, powdered willow bark - an early form of aspirin), which has been shown to cause papillary necrosis if taken in large amounts. It is fair to say then, that in the absence of any other evidence of hypertension or diabetes, Beethoven likely died from papillary necrosis (end-stage kidney failure) resulting from a combination of liver cirrhosis and analgesic nephropathy.
As for Beethoven's deafness, it was probably otosclerosis, an abnormal growth of the bones in the middle ear whose causes are not entirely understood but seem to be at least partially hereditary.
Yay, my girlfriend is in medical school.