A patient presents with heterotopic ossification around the knee joint. The laboratory investigation of choice in him is?
A. Alkaline phosphatase
B. Serum calcium
C. Serum acid phosphatase
D. Serum potassium
(Repeat question – AIPGMEE 07 – MK q261)
Correct answer : A. Alkaline phosphatase
Alkaline phosphatase has been recommended as a useful screening tool for HO. Alkaline phosphatase levels become abnormal approximately 2 wk after injury. In the typical case of HO, the alkaline phosphatase levels reached approximately 3.5 times the normal value 10 wk after the inciting trauma, before returning to normal at approximately 18 wk.. Unfortunately, alkaline phosphatase levels cannot be used to draw clinical conclusions about maturity or recurrence of HO: Values may be normal in the presence of active HO or may remain elevated for years, calling into question whether maturity has been reached at all. Nonetheless, this inexpensive and easily obtained test is frequently used to detect early HO.
Recently, measurement of the 24-h PGE2 urinary excretion has been recommended as a valuable indicator of early HO. A sudden increase in PGE2 excretion points to the need for bone scans to qualify the process. The PGE2-blocking agent indomethacin is effective in slowing the HO disease process, and indomethacin is therefore useful in treating HO.