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TETANY |
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due to alkalosis (which lowers serum ionised calcium): |
persistent vomiting excess alkali intake (usually with renal impairment)hyperventilation Conn's syndrome (very low potassium causes H+ loss) |
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due to hypocalcaemia: |
inadequate intake of calcium or vitamin D malabsorption other causes of vitamin D deficiency hypoalbuminaemia low PTH (see causes of hypoparathyroidism)citrated blood transfusions (chelation of calcium) (concomitant acidosis usually prevents tetany) (saponification of calcium)following surgery for parathyroid adenoma ('hungry bones syndrome')distal renal tubular acidosis hypomagnesaemia [causes same features as hypocalcaemia]cis-platinum |
NB: tetany should be differentiated from:
strychnine poisoning
(flaccidity occurs between convulsions)severe meningitis with neck / back stiffness
(opisthotonus)epilepsy / fit
(tonic phase)tetanus
(persistent spasm)hysteria
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