Tendon xanthomas

This is a common MRCP exam question. My friend just got this 1 week ago when sitting for the exam in Singapore.

There are 2 differential diagnosis that you have to think about
1) Chronic tophaceous gout
2) Tendon xanthomas

The question is how to differentiate both of them. One simple test is that tendon xanthomas move with the tendon. So ask the patient to move the finger and feel the lesions and see whether it moves with the tendon.
Look also at the distribution of the deposits, in tendon xanthomas over the knuckles, elbows, knees, Achilles tendon. Look also for xanthalesma.
For gouty tophi, look at the ear lobes, feet, elbows.

Comment
Tendon xanthomas are seen in 75% of adults with familial
hypercholesterolaemia. They are intra-and extra-cellular
accumulations of cholesterol, noticed on extensor
tendons over knuckles, achilles, knee, and elbows. They
decrease with treatment of hypercholesterolaemia. They
are also seen in familial defective apo B100, type 3
hyperlipoproteinaemia, and sitosterolaemia

Reference
1. Mahley RW, Weisberger KH, Farese RV. Disorders of Lipid
Metabolism in Wilson JD, Foster DW, Kronenberg HM, Larsen
PR (eds). William’s Textbook of Endocrinology (9th ed).
Philadelphia, WB Saunders 1998; 23: 1099-1153.