Abnormal calcium metabolism in normocalcaemic sarcoidosis

Abstract

Abnormal calcium metabolism in normocalcaemic sarcoidosis SIR,-In their otherwise excellent paper on calcium metabolism in sarcoidosis (18 December, p 1473) Dr M Reiner and his colleagues state that total hydroxyproline excretion is increased in acute sarcoidosis and that this indicates increased bone resorption.So far as I know the site of origin of the excess hydroxyproline has never been determined. Although it would seem logical that it is due to increased bone turnover there are at least three other possibilities: (1) It could be due to increased turnover of collagen in the lung parenchyma. (2) It could arise from the sarcoid granulomata themselves-significant amounts of hydroxyproline have been detected in experimental granulomata.' (3) Theoretically it could be due to excess turnover of the Clq component of complement. Total complement levels have been shown to be elevated in sarcoidosis,2 $ particularly in the acute phase.L astly, though the reference they quote) and also the work of Pawelec" did show elevated levels of urinary hydroxyproline in sarcoidosis, at least one large series7 failed to show any increase over control values. I would therefore be chary at present of adducing raised hydroxyproline values as confirmation of the degree of bone involvement in sarcoidosis.