2011 PREP SA on CD-ROM
Question: 74
A 9-month-old girl is brought to the emergency department by her middle eastern immigrant
parents, who have observed an episode of twitching of her extremities. On physical examination,
the infant has prominent wrists (Item Q74) and ankles and an open fontanelle. The parents tell
you through an interpreter that she is exclusively breastfed and neither she nor her mother takes
vitamins. You note that the mother is partially veiled.
Of the following, the MOST likely cause of the twitching is
A. hypercalcemia
B. hypocalcemia
C. hypomagnesemia
D. hypophosphatemia
E. vitamin D deficiency
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2011 PREP SA on CD-ROM
Question: 74
(Courtesy of M Rimsza)
Prominent wrists, as described for the infant in the vignette.
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2011 PREP SA on CD-ROM
Critique: 74
Preferred Response: B
The child described in the vignette has clinical signs of rickets, and her mother is protected
from sunlight by veiling. Neither mother nor child takes supplemental vitamins. Therefore, the
child likely has vitamin D deficiency as a result of poor stores at birth and continued poor vitamin
D intake and production. However, vitamin D deficiency alone does not cause the twitching
reported for the girl. Twitching is a sign of hypocalcemia caused by vitamin D deficiency.
Hypocalcemia induces neuromuscular irritability that can manifest as a positive Chvostek
sign, carpopedal spasm, or a positive Trousseau sign. Approximately 10% of individuals who
have normal calcium concentrations have positive Chvostek signs. A positive Trousseau sign is
induced by the tissue hypoxia caused by a tight blood pressure cuff and causes enough
discomfort that this test rarely is performed when a laboratory assessment of calcium is so
easily confirmatory. Severe hypocalcemia induces paresthesias (oral, finger, and toe tingling),
twitching, and seizures. Hypocalcemia also can lead to diarrhea. One of the most common
causes of hypocalcemia is vitamin D deficiency rickets, either when it is very severe or during
the initial phases of recovery when calcium is being taken up rapidly by healing bone.
Hypercalcemia can cause slowed mentation, stupor, constipation, polyuria, renal calculi, and
extreme thirst but does not cause twitching. Hypomagnesemia may cause neuromuscular
irritability similar to that seen in hypocalcemia but is much less common and is accompanied by
nausea and loss of appetite. Magnesium interferes with release of stored parathyroid hormone
and, therefore, can cause hypocalcemia. The signs and history typical for vitamin D deficiency
rickets reported for this girl make this less probable. Hypophosphatemia causes muscle
weakness and changes in mental status. It also may be seen in rickets but is not associated
with neuromuscular irritability.
Suggested reading:
Agus Z. Clinical manifestations of hypercalcemia. UpToDate Online 17.3. 2009. Available at:
http://www.utdol.com/online/content/topic.do?topicKey=calcium/5007&selectedTitle=4%7E150&s
ource=search_result4
Agus ZS. Diagnosis and treatment of hypophosphatemia. UpToDate Online 17.3. 2009.
Available at:
http://www.uptodateonline.com/online/content/topic.do?topicKey=calcium/5885&selectedTitle=37
%7E150&source=search_result
Agus ZS. Diagnosis and treatment of hypomagnesemia. UpToDate Online 17.3. 2008. Available
at:
http://www.uptodateonline.com/online/content/topic.do?topicKey=calcium/5547&selectedTitle=9
%7E150&source=search_result
Fitzpatrick LA. Hypocalcemia: diagnosis and treatment. Endotext.org. 2002. Available at:
http://www.endotext.org/parathyroid/parathyroid7/parathyroid7.htm
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2011 PREP SA on CD-ROM
Misra M, Pacaud D, Petryk A, Collett-Solberg PF, Kappy M; Drug and Therapeutics Committee of
the Lawson Wilkins Pediatric Endocrine Society. Vitamin D deficiency in children and its
management: review of current knowledge and recommendations. Pediatrics. 2008;122:398417. DOI: 10.1542/peds.2007-1894. Available at:
http://pediatrics.aappublications.org/cgi/content/full/122/2/398
Singhai A, Campbell DE. Hypocalcemia. eMedicine Specialties, Pediatrics: General Medicine,
Endocrinology. 2009. Available at: http://emedicine.medscape.com/article/921844-overview
Wagner CL, Greer FR; Section on Breastfeeding and Committee on Nutrition. Prevention of
rickets and vitamin D deficiency in infants, children, and adolescents. Pediatrics. 2008;122:11421152. DOI: 10.1542/peds.2008-1862. Available at:
http://pediatrics.aappublications.org/cgi/content/full/122/5/1142
Copyright © 2010 by the American Academy of Pediatrics
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