Lesson of the Week: Hypocalcaemic stridor and infantile nutritional rickets
BMJ 1995; 310 doi: https://doi.org/10.1136/bmj.310.6971.48 (Published 07 January 1995) Cite this as: BMJ 1995;310:48
- a Department of Anaesthesia, Hospitals for Sick Children, Great Ormond Street, London WC1 3JN
- b Department of Paediatrics, Queen Elizabeth Hospital for Children, London E2 8PS
- Correspondence to: Dr Sury.
- Accepted 7 April 1994
Nutritional deficiency of vitamin D is considered to be a rare cause of rickets in industrialised countries, mainly because vitamin D is added routinely to formula feeds for infants.1 2 Human breast milk, however, may be deficient in vitamin D, and exclusively breast fed infants who have not received vitamin supplements are at risk. Otherwise well nourished infants may not have the obvious or typical bony deformities of rickets but may present with the symptoms of hypocalcaemia. We describe two infants who presented with stridor and intermittent sudden airway obstruction due to laryngospasm. Both infants had severe hypocalcaemia due to nutritional deficiency of vitamin D.
Case reports
CASE 1
A 5 month old black boy weighing 7.5 kg was taken to the accident and emergency department at Queen Elizabeth Hospital for Children with a one month history of intermittent laboured and noisy breathing. The boy's respiratory distress had often been accompanied by generalised rigidity, convulsions, and cyanosis and had usually occurred when he was crying. He was taken to the hospital because he had become apnoeic at home and had been given mouth to mouth resuscitation by his mother. Just after he was admitted he became distressed and stridulous. Convulsions followed, which were treated with rectal paraldehyde. He had enlarged tonsils, and a nasopharyngeal airway seemed to relieve the airway obstruction partially. Initially the convulsions were thought to be caused by hypoxaemia, and a tonsillectomy was proposed. The plasma calcium concentration, however, was 1.15 mmol/l, and vitamin D deficiency and rickets were diagnosed from the results of biochemical tests and an x ray examination. The boy was successfully treated with intravenous calcium gluconate followed by oral calcium and vitamin D supplements.
CASE 2
A 7 month old black boy weighing 7.5 kg was brought to the same hospital one year later. His general practitioner had referred him for investigation of upper airway noises and recurrent respiratory infections, which he had had for three months. According to his parent, a sibling had had his “narrowed windpipe” surgically corrected.
The boy was tachypnoeic and had both inspiratory and expiratory stridor. Coarse chest crepitations were heard on auscultation, and a chest x ray film showed atelectasis of the left upper lobe. The stridor became worse. Examination of the oropharynx caused crying followed by complete upper airway obstruction and generalised convulsions, which were successfully treated with continuous positive airway pressure and rectal diazepam. Examination of the larynx under anaesthesia was proposed. Tetanic spasms of the arms were observed, however, and hypocalcaemia was suspected. The plasma calcium concentration was 0.9 mmol/l and the QTc interval (rate corrected) of 0.52 s (normal range 0.35-0.44 s) in an electrocardiogram was prolonged. An intravenous infusion of calcium gluconate was started and vitamin D supplements were given. Biochemical investigations and x ray examinations confirmed vitamin D deficiency and rickets.
RESULTS OF BIOCHEMICAL TESTS
The table shows the results of the biochemical tests in both cases, which confirmed the diagnoses of vitamin D deficiency. Both boys had been exclusively breast fed. Typical features of rickets were seen in the x ray films for both infants, including splaying of long bone metaphyses, expansion of the joints, and widening of the anterior ends of ribs. Acute respiratory symptoms resolved within hours of treatment being started. Plasma calcium concentrations gradually increased and were in the normal range by 10 days in case 1 and 13 days in case 2.
Results of biochemical tests done in two black infants aged 5 and 7 months who were admitted to hospital with stridor and intermittent sudden airway obstruction. Reference ranges are given in parentheses
Discussion
Vitamin D deficiency is a rare cause of hypocalcaemia and tetany,2 and, although the causes of paediatric stridor are well known, with 80% of cases being due to infection,3 hypocalcaemia may be overlooked.4 Fortunately, in both of these cases severe hypocalcaemia was diagnosed in time for surgical intervention to be prevented.
Both infants were at risk of developing rickets: they had been exclusively breast fed, were black, and lived in an inner city area.1 5 Typically, term infants with an inadequate nutritional intake of vitamin D may present at between 3 and 6 months of age and are at risk, particularly during the winter.2 5 Vitamin D supplements are recommended for lactating mothers and for children up to the age of 2 years.5 6 7
In infants and small children the features of vitamin D deficiency include lethargy, recurrent respiratory infections, stridor, tetany, convulsions, and rickets.1 8 Infants who are too young to walk will not develop the limb deformities of rickets, such as genu varum. Hypocalcaemia reduces myocardial contractility and may result in arrhythmias and left ventricular failure. Cardiac tetany, although rare, is often fatal. An electrocardiogram with a prolonged QTc interval may indicate hypocalcaemia before biochemical investigations are done.
Hyperventilation reduces the arterial carbon dioxide partial pressure and causes the plasma pH to increase. The plasma concentration of ionised calcium then decreases and may cause carpopedal spasm and tetany. Laryngospasm related to exercise was described in a child with hypocalcaemia, and a similar mechanism was suggested.9 Crying, and consequent hyperventilation, may worsen existing stridor of any aetiology but may also cause tetany and laryngospasm when hypocalcaemia is present.
If infants are exclusively breast fed and their mothers are not given dietary supplements of vitamin D then the infants may develop rickets, become severely hypocalcaemic, and present with acute respiratory symptoms. The plasma calcium concentration should be measured urgently. Infants with severe hypocalcaemia may suddenly develop laryngospasm and should be treated urgently in a department where, if necessary, they can receive prompt tracheal intubation.
We thank Mr D Albert and Professor C B S Wood for their permission to report these cases.