Is hyperphosphatemia an independent cause of tetany?

Type of article: Letter to the Editor

Harsha Halahalli, Department of Physiology, KS Hegde Medical Academy, Mangalore, India

Received 20 January 2008; accepted 20 January 2008.

Singh has rightly pointed out [1] that hyperphosphatemia could also trigger muscular spasms. Hyperphosphatemia could result from several causes such as impaired renal function, tissue necrosis, rhabdomyolysis, tumor lysis syndrome, and exogenous administration of phosphate commonly in the form of laxatives. If phosphate builds up rapidly in such situations, it may be associated with features of tetany. However, in such cases the tetany is due to the hypocalcemia that results from the excess phosphate levels and in that sense, hyperphosphatemia may not be an independent cause for tetany [2].

Milk-alkali syndrome is not always accompanied by hyperphosphatemia [4]. Unfortunately, in the case report by Goetz [3], serum phosphate levels at the time of admission are not reported and those reported for the sixth day after admission are within normal limits. The tetany observed in this case despite the hypercalcemia could be attributed to the accompanying alkalosis which is known to reduce ionized calcium levels. It is possible that the level of ionized calcium which modulates membrane excitability is sufficiently low so as to cause tetany even though total serum calcium is moderately elevated.

Thus, my interpretation is that hyperphosphatemia could be associated with tetany only if it were also accompanied by reduced serum levels of ionized calcium.

Was the tetany in the case report by Goetz [3] due to hyperphosphatemia? Well, it is questionable.

Conflict of interests: none

References:

[1] Singh S. Milk alkali tetany. Medical Physiology Online 2008 [Link], accessed 20 January 2008

[2] Domico MB, Huynh V, Anand SK, Mink R. Severe hyperphosphatemia and hypocalcemic tetany after oral laxative administration in a 3-month-old infant.
Pediatrics. 2006; 118: e1580-1583.

[3] Goetz AA. Milk-alkali syndrome with jaundice and tetany. California Medicine 1958; 89: 136-139

[4] Felsenfeld AJ and Levine BS. Milk alkali Syndrome and the dynamics of calcium homeostasis. Clin J Am Soc Nephrol 2006; 1: 641–654.

Reviewed by E.S.Prakash, Editor, Medical Physiology Online.