A 5-month-old with failure to thrive

A 5-month-old girl was referred for failure to thrive and symptoms of bronchiolitis. Her history revealed that she was born at term from an uncomplicated pregnancy, with a birth weight of 3.22 kg (50th percentile). Her family history was unremarkable and her medical background was only significant for an episode of bronchiolitis at the age of 3 months, for which she had not been hospitalized. At that time, she weighed 5.55 kg (15th percentile). Following that episode, respiratory symptoms had resolved. However, feeding difficulties had been noted over the 2 months preceding presentation. Two days before admission she developed nasopharyngeal secretions and had an increased cough. The baby had never experienced vomiting or diarrhea. On physical examination, she weighed 4.69 kg (0.1th percentile). She was not dysmorphic, but was sleepy and almost unresponsive to examination. Her blood count was found to be within normal limits. Her blood gas as well as her electrolytes were abnormal as described in Table 1. Investigations summary Investigations summary The chest radiography showed a small pulmonary infiltrate of the right upper lobe. Her electrolytes disturbances were quickly corrected with intravenous fluids. The final diagnosis was established with further testing. Given the clinical presentation of metabolic alkalosis, a sweat test was performed and revealed to be elevated on multiple occasions. A diagnosis of cystic fibrosis (CF) was made and the cystic fibrosis transmembrane conductance regulator (CTRF) gene analysis showed that the patient was heterozygous for two pathogenic mutations, Delta F508 and p.A455E. The latter is characterized by normal pancreatic function and less severe lung damage. Currently, CF is not part of the routine newborn screening available in all Canadian provinces, which was the case for our patient. CF is the most common fatal genetic disease among children and young adults in Canada, with Delta-F508 being the most common mutation found worldwide. Disease occurs when there are two CF defective alleles. The result is abnormal regulation of chloride channels in sweat glands, airways, pancreas and intestine. A distinctive feature of this patient is the initial clinical manifestation of the disease with a Pseudo-Bartter syndrome (PBS). Classic Bartter syndrome is an autosomal recessive disorder affecting the renal tubules that often presents in childhood and which is mainly characterized by metabolic alkalosis, hyponatremia, hypokalemia and hypochloremia. Bartter syndrome was a consideration at presentation, but no recurrence of electrolyte imbalance was observed with discontinuation of intravenous fluids. In CF, the dysfunction in the CTRF gene in sweat glands leads to an excessive electrolytes and water loss. As a result of extracellular volume contraction and the loss of electrolytes, there is a stimulation of the renin-angiotensin-aldosterone system. The activation of the renin-angiotensin-aldosterone system eventually leads to an increased loss of potassium and reabsorption of bicarbonate in renal tubules. PBS can easily be misdiagnosed as severe dehydration or classic Bartter Syndrome. In the latter, there is renal tubular damage and persistent electrolytes loss in urine, unlike in Pseudo-Bartter Syndrome. In the present case, our patient’s electrolytes and blood gas were rapidly corrected with intravenous fluids and no further episodes of such anomalies were found upon discontinuation of fluids, confirming the absence of tubular dysfunction and renal losses. Retrospective case series on PBS as a clinical presentation of CF were conducted mainly in Middle East and Europe. This condition can occur at the initial presentation of CF in regions where neonatal screening is not available, but it is often a complication of the disease. Associations have been made with situations where there is an increased sodium loss, as during warm summer periods (1). In fact, patients with CF have a higher sodium requirement due to additional losses through sweat, especially in hot weather, exercise or periods of illness and current recommendations advise consideration of sodium supplementation in these circumstances (2). Pseudo-Bartter syndrome also often coexists with acute respiratory exacerbations. The principal way to support these patients is by correcting their electrolytes disturbances and their level of hydration, and by looking for contributing factors, such as infections. There are several other conditions to consider in the evaluation of a baby with this clinical picture of electrolyte imbalance and metabolic alkalosis. First, one should consider gastrointestinal losses as seen with chronic diarrhea or in severe cases of vomiting, such as pyloric stenosis. Indeed, the classic presentation of pyloric stenosis, apart from projectile and nonbilious vomiting, is metabolic alkalosis with hypochloremia and hypokalemia. Furthermore, renal losses should also be considered in the setting of mineralocorticoid excess, diuretic use or primary renal diseases. Our patient is now 18 months old. There was no recurrence of PBS since the diagnosis. Her growth is normal without pancreatic enzymes but with daily sodium supplementation. CF may present with metabolic alkalosis and electrolytes abnormalities that may be confused with pyloric stenosis or primary renal disease. Patients with CF, especially during infancy, are at risk for hyponatremic dehydration under conditions of stress and sodium chloride supplementation needs to be considered. Since CF is a common disease among Canadians, clinicians must consider this diagnosis in the presence of failure to thrive, even without respiratory symptoms. One should keep in mind that not all Canadian provinces currently screen for CF as part of their newborn screening program.

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