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An African American infant has cardiomyopathy and hypocalcemia and is facing a possible transplant. Final diagnosis is rickets.
It's another busy Friday morning, and you are on call in the pediatric intensive care unit. Cardiology is transferring an extremely ill infant from an outside hospital. The patient reportedly has severe dilated cardiomyopathy and is sent to your tertiary care center for treatment-and consideration of a heart transplant evaluation.
Upon arrival, you review the patient's accompanying medical records. She is a previously healthy 4-month-old African American infant who presented to the outside hospital with a one-day history of tachypnea. She was otherwise asymptomatic and acting normally. Her past medical history is unremarkable. Pregnancy and delivery were uncomplicated. Growth and development are normal. She is exclusively breastfed. She has been feeding well and stooling normally. The patient is on no medications or supplements. There is no family history of childhood pulmonary or cardiac disease.
At the outside hospital, a chest X-ray was ordered because of her increased respiratory rate. The X-ray showed significant cardiomegaly. The lungs were normal. Because of the cardiomegaly, a twelve-lead ECG and an echocardiogram were done. The ECG was normal, with the exception of repolarization changes consisting of T-wave inversion in the lateral precordial leads indicative of left ventricular strain. The echocardiogram showed dilated cardiomyopathy, with markedly reduced left ventricular systolic function. The estimated ejection fraction was abnormally low, at 25%. There was also moderate mitral valve regurgitation. There was no evidence of congenital heart disease.
You examine the patient. She is sedated and intubated on a ventilator. She is afebrile. Her heart rate is 155 bpm. Her blood pressure is 83/32 mm Hg in her left arm. Her oxygen saturation is 99% on 30% FiO2.
She appears well nourished and well developed. Her weight is 6.8 kg (75th percentile). Her height is 63 cm (50th percentile). She has no dysmorphic features. She is not cyanotic. The lungs are clear to auscultation. The precordium is not active. First and second heart sounds are normal. There is an apical gallop. A grade 2/6 systolic murmur is heard at the apex, radiating toward the left axilla. Proximal and distal pulses are 2+. Capillary refill is less than two seconds in the upper extremities and delayed at three seconds in the lower extremities. The liver edge is palpable 3 cm below the right costal margin in the midclavicular line. There is no spleno megaly. The upper extremities are warm. The patient's lower extremities are cool below the knees. There is no peripheral edema.
Why is her heart failing?
The differential diagnosis for dilated cardiomyopathy in this patient is extensive. You begin to review her lab results from the outside hospital. One particular result grabs your attention. The patient's serum calcium level was very low, at 5.6 mg/dL (normal is 8.0 to 10.6 mg/dL) and albumin was low to normal at 3.5g/dL (3.5 to 5 g/dL). This abnormality is of particular interest to you because of the important role calcium plays in cardiac muscle contraction. Could the patient's dilated cardiomyopathy be secondary to the profound hypocalcemia? Would her cardiac function improve with correction of the hypocalcemia?
A review of the medical literature showed several reports of cardiomyopathy in adults and children secondary to hypocalcemia that was reversible with correction of the calcium. Most cases in adults were due to hypoparathyroidism.1-5 There were several reports of cardiomyopathy in children with rickets,6-12 though only one was in the United States.6 Of note, the only patient previously reported in the United States was also an exclusively breastfed 5-month-old African American infant. A review of the cases showed a favorable outcome over months, with resolution of hypocalcemia and correction of rickets.
But why is her calcium so low?
You begin to investigating why this patient could have hypocalcemia. The core differential diagnosis includes:13