tophus
n.,
pl. 3phi 73fj8 5L, tufa6 Med. an abnormal mineral deposit, as of calcium carbonate, about the joints, on the roots of the teeth, etc., in a person who has the gout; chalkstone

URL about gout:http://www.highlands-ortho.com/gout.html#diagnosis

How Gout Is Diagnosed
A combination of medical history and laboratory studies is necessary to make a definitive
diagnosis for gout. The following procedures are usually used:

Medical history and physical examination by your physician.
Appropriate laboratory tests to check the blood's uric acid level and the presence of uric
acid crystal deposits in the affected joint. These are the diagnostic markers.
Systematic exclusion of differential diagnoses like pseudogout.
Possibly an X-ray study, to evaluate extent of joint damage.

This once I think the dictionary is in grievous error. In gout the deposits are of uric acid or urates.
Where in "Tophet" did the editors get the above misinformation?
As a bit of trivia, the Dalmation coachhound is the only other mammal similarly afflicted.