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The case of a bow legged toddler.

A 34-month-old African American male was referred for evaluation of anteromedial bowing of the legs (Fig. 1). Pronounced widening of the wrists and beading of the ribs at the costochondral junctions were also confirmed by X-ray. He was breast-fed until 2 years of age. He had eczema, but no other significant medical or family history. The patient was noted to drink minimal milk, eat little fish or eggs, and spend little time outdoors. The pertinent laboratory results are listed in Table 1.

[FIGURE 1 OMITTED]

QUESTIONS

1. The clinical and biochemical findings (Table 1) are consistent with what diagnosis?

2. What is the potential therapy, and how is it monitored?

The answers are below.

ANSWERS

The patient was diagnosed as having hypovitaminosis D (rickets). Caused by dietary insufficiency, dark skin, and minimal sun exposure, vitamin D deficiency is treated with 25-hydroxyvitamin [D.sub.2] or [D.sub.3] supplementation. Compliance and efficacy are monitored with [D.sub.2] and [D.sub.3] measurements. The 1,25-dihydroxyvitamin D concentration is unreliable for making a primary diagnosis of hypovitaminosis D because it depends on the activity of 1a-hydroxylase (which converts 25-hydroxyvitamin D into the active 1,25-dihydroxyvitamin D), which is regulated by calcium, phosphate, and parathyroid hormone (PTH). Plasma calcium and phosphate are typically decreased, but can be normal in vitamin D deficiency rickets. PTH stimulates mobilization of these minerals from osteoclasts, a mechanism that acts to maintain blood calcium stores by sacrificing bone.

Three months of [D.sub.2] supplementation showed resolution of leg bowing and a total 25-hydroxyvitamin D of 32 [micro]g/L ([D.sub.2], 23 [micro]g/L [D.sub.3], 9 [micro]g/L).

Armanda D. Tatsas and Alison Woodworth *

Department of Pathology, Vanderbilt University Medical Center, Nashville, TN.

* Address correspondence to this author at: Department of Pathology, Vanderbilt University Medical Center, 4918EA TVC, 1301 Medical Center Dr., Nashville, TN 37232-5310. Fax 615-343-9563; e-mail Alison.Woodworth@Vanderbilt.Edu.

DOI: 10.1373/clinchem.2009.131516
Table 1. Laboratory results for the patient.

Analyte Patient result Reference interval

Calcium 9.8 mg/dL 8.5-10.5 mg/dL
 (2.4 mmol/L) (2.1-2.6 mmol/L)
Intact PTH 68 pg/mL 10-65 pg/mL
 (7.2 pmol/L) (1.1-6.8 pmol/L)
Phosphorus 5.1 mg/dL 2.5-4.5 mg/dL
 (1.6 mmol/L) (0.8-1.5 mmol/L)
 [4.3-6.3 mg/dL
 (1.4-2.0 mmol/L)] (a)
25-Hydroxyvitamin D 13 [micro]g/mL 30-80 [micro]g/mL
1,25-Dihydroxyvitamin D 89 ng/L 15-75 ng/L

(a) Interval age adjusted for 3 years.
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Title Annotation:Clinical Chemist: What Is Your Guess?
Author:Tatsas, Armanda D.; Woodworth, Alison
Publication:Clinical Chemistry
Date:Oct 1, 2009
Words:432
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