Hypocalcemic Rachitic Stridor: A Neglected Warning Sign in Infants

Although stridor is a common respiratory symptom associated with upper respiratory diseases, yet its relation with hypocalcemia is not widely appreciated. The mechanism of hypocalcemia in causing stridor might be a collapsing of larynx most likely caused by decalcification due to hypocalcemia. Vitamin D deficiency causes a reduction in serum calcium, which stimulates the production of extra PTH to mobilize and maintain calcium from bone and cartilage for more vital cells of the body, brain, heart and blood. Stridor might appear with upper respiratory tract infection, accordingly the role of hypocalcemia as a cause of stridor might not be recognized. Infants are born with poor vitamin D in places with high prevalence of vitamin D deficiency due to environmental, social, customs and housing factors. Due to maternal vitamin D deficiency, breast milk is low in vitamin D which leads to poor absorption of calcium. Stridor caused by hypocalcemia should be considered as a warning sign to prevent more serious complications as cardiomyopathy, myelofibrosis, and convulsions. In communities with high prevalence of vitamin D deficiency checking for hypocalcemia should be part of the work up, when stridor is the presenting symptom in infants. The mechanism by which hypocalcemia causes stridor might be laryngiomalacia.

Introduction

Stridor is a noisy breathing in infants or older children, usually frightening to parents. John Apley [1] said while answering a question what is strider:

“For an answer, I consulted not only doctors and dictionaries, but also parents and poets. The word strider is derived from Latin strider, to make gratingly shrill or harsh noise. It needs to be harsh and vibrating, though it should be sustained or repeated, mothers tell me that their child coos like a dove, or purrs like a cat or grunts like a piggy or makes a wheezing, grunting, or sieving noise. Thackeray writing of the healthy baby who would crow with delight is my exemplars for my theme is that in the diagnosis of strider we should consider more than the noise. The high-pitched crowing sound of laryngospasm due to tetany may be diagnosed as laryngeal stridor. The mistake is most likely in tetany of the newborn, but it may be made also in older children with increased neuromuscular instability, provoked by a state of alkalosis, whether due to celiac disease, rickets, hypoparathyroidism, renal failure or hyperventilation.”

Stridor is an abnormal high-pitched sound produced by turbulent airflow through a partially obstructed airway at the level of the supraglottis, glottis, subglottic, and/or trachea. The tonal characteristics of the sound are extremely variable (IE, harsh, musical, or breathy); however, combined with the pace, volume, duration, rate of onset, and associated symptoms, the tonal characteristics may provide additional diagnostic clues. In all cases, it should be differentiated from the startle, which is a lower-pitched, snoring-type sound generated at the level of the nasopharynx, oropharynx, and, occasionally, supraglottic.

Stridor is a symptom, not a diagnosis or disease, and the underlying cause must be determined. Stridor may be inspiratory, expiratory, or biphasic depending on its timing in the respiratory cycle. Inspiratory stridor suggests a laryngeal obstruction, while expiratory stridor implies tracheobronchial obstruction. Biphasic stridor suggests a subglottic or glottis anomaly. In addition to a complete history and physical, as well as other possible additional studies, most cases require flexible and/or rigid endoscopy to evaluate the etiology of stridor adequately.

As we see many cases of nutritional rickets, in which hypocalcemic convulsions is the commonest presentation in the first year of life [2] and as it might be associated with other rare complications as cardiomyopathy [3] and myelofibrosis [4] and as well as iron deficiency anemia [5] and as stridor is a serious complication jeopardizing respiration and as hypocalcemia due to vitamin D deficiency is not uncommon, it is reviewed in this communication.

Review and Results

PubMed was reviewed for stridor and hypocalcemia. It revealed 22 publications which were reviewed, 15 out of these publications were discussing the association between stridor and hypocalcemia of which two were in elderly people and the rest were mostly case reports in infants as described in table 1. Most of them were male aged between a few days to 16 months. Stridor was the presenting feature in all cases with or without convulsions, but all were having hypocalcemia. These cases were reported from a wide range of countries, but the cases in temperate countries were among immigrants from Africa, Asia or Hispanics. The ages in the majority were under one year and all were breastfed. Two were elders one with previous thyroidectomy leading to chronic hypocalcemia and stridor.

General causes of stridor

Noisy breathing to be termed stridor was observed in laryngeo-tracheo -bronchitis, foreign body, laryngiomalacia and many other congenital and acquired causes. The cause which is discussed in this communication is not given in Medscape, may be because it is rare.

Hypocalcemia as a cause of stridor in medical literature is shown in the table. Four reports from each of USA, and UK. In addition, two from each of Spain, and India and one from Taiwan. These infants were six boys and one girl and the rest were introduced as infants without giving their gender. All were dark skinned living in temperate countries. The ages of the infants varied from eight days to 17 months at presentation and their mean age was 7.5 months. All presented with stridor and respiratory distress and all were found to have hypocalcemia with high alkaline phosphatase and PTH. There was clinical evidence of rickets in older infants.

Pathophysiology of stridor in hypocalcemia

The narrowing of the upper part of the respiratory tract causes a turbulence of air flow manifested as stridor, usually observed in upper respiratory tract infection or foreign body inhalation [5].

As we are seeing rising cases of rickets presenting with hypocalcemia and occasionally with stridor that might be misdiagnosed as viral croup, I am reviewing the relation between stridor and hypocalcemia. Although stridor is a common respiratory symptom associated with upper respiratory diseases, yet its relation with hypocalcemia is not widely appreciated. The mechanism of hypocalcemia in causing stridor is most likely a sort of laryngeal collapse due to loss of its rigidity caused by hypocalcemia which is obvious in the early phase of rickets. In infancy rickets starts with hypocalcemia due to lack of vitamin D. In this phase the bony features of rickets are not obvious. It is when the parathyroid glands are stimulated by the hypocalcemia that an excess of parathormone mobilizes the calcium from the bones and cartilage leading to decalcified bones and softening of cartilage, which in this phase present as stridor due to collapse of the larynx. Narrowing associated with edema, foreign body, or pressure from outside in addition to softening and narrowing of the larynx due to hypocalcemia is what is causing stridor, also aggravated by upper respiratory infections, that is why the role of hypocalcemia in stridor is not well appreciated. Hypocalcemia stimulates parathyroid glands to secrete extra hormone needed to mobilize calcium from bone and cartilage with a more vital objective to maintain enough calcium for brain, heart and blood. In places with prevalence of vitamin D deficiency, breast milk is low in vitamin D due to maternal vitamin D deficiency. Stridor caused by hypocalcemia should be recognized early and treated promptly taken as a warning sign of occult rickets that might herald serious complications as convulsions [2], cardiomyopathy [3] and myelofibrosis [4]. The development of stridor is not as common as the other features of rickets. Due to the hyperpathyroidism playing a major role in correcting the blood level of calcium.

Bronchogenic cyst

Bronchogenic cysts as a cause of stridor has been reported from different parts of the world. All of them presented with noisy breathing since birth with variable degrees. Ironically, a case was diagnosed following a peanut aspiration which was taken as the cause of stridor which persisted after surgical removal to diagnose the primary cause of stridor. The details are shown in table 2. All improved with the disappearance of stridor post operatively. This is a rare curable cause of stridor. Although hypocalcemia is not a common cause, it is essential to think of it together with other common causes of stridor, specially these mostly congenital cases presents as early as the first day in life, in contrast to hypocalcemic might be observed after the first week of life [6].

Other causes of stridor

There are many causes of stridor as shown in table 3 which might be acute or chronic with some of them being very serious with high mortality and needs urgent recognition and prompt management. Stridor in infants can be life threatening and pedrtricans and all prctioners and all medical assistants need to be aware of managing this problem. Hypocalcemia as a cause of stridor need to be thought of, as it dramatically responds to calcium and vitamin D therapy in adequate doses. As we are concentrating on hypocalcemic stridor [7], in this communication other causes were not discussed in details.

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