Case 1: A toddler with recurrent chest problems

A 19-month-old boy presented to the emergency room with a five-day history of progressive cough and nasal congestion. On the day of admission, he had an increased respiratory rate with distress and audible wheezing, a two day history of fever and a poor appetite with decreased urine output. His parents also noted pale, loose stools and no vomiting. He was born at term after an uncomplicated pregnancy. His birth weight was 3.52 kg (50th percentile). He was diagnosed with ‘asthma’ at five months of age and has had five ‘asthma exacerbations’, none of which required hospitalization. He was treated with salbutamol and inhaled steroids. He also had four previous episodes of otitis media. On examination, he looked pale and tired. His weight was 10 kg (third to 10th percentile) and height was 83 cm (just below 50th percentile). He was tachypneic with a rate of 50 breaths/min to 60 breaths/min with moderate respiratory distress. He was having severe paroxysms of cough lasting 2 min to 3 min, and he had bilateral wheezing with no crackles. His heart rate was 140 beats per minute and the cardiovascular exam was otherwise normal. His abdomen was mildly distended but soft and nontender. There was no hepatosplenomegaly. The rest of the physical examination was within normal limits. Chest x-ray revealed hyperinflation with bibasilar coarse bronchovascular markings. The patient was admitted with a diagnosis of ‘asthma exacerbation’; and therapy was initiated with inhaled salbutamol and systemic steroids. With this treatment, he gradually improved from a respiratory point of view. While in hospital, further investigations were initiated that revealed his underlying problem. Because of the history of abnormal stools and slow weight gain, a malabsorption work-up was performed. Examination of the stool under the microscope using Sudan Red stain revealed fat globules and a three-day fecal fat collection confirmed fat malabsorption. The sweat chloride was elevated at 99 mmol/L (normal is less than 60 mmol/L). Vitamins A and E levels were both decreased. The patient was diagnosed with pancreatic-insufficient cystic fibrosis (CF). Treatment consisted of a 10-day course of antibiotics, regular salbutamol and chest physiotherapy. Pancreatic enzymes and vitamin ADEK were initiated. CF is the most common fatal genetic disorder in North America. It has an incidence of one in 2500 among Caucasians. It is less common in people of African (one in 17,000) and Asian (one in 90,000) descent. It involves a single gene defect on chromosome 7 that encodes the CF transmembrane conductance regulator protein. This protein resides on the apical membrane of epithelial cells lining the airways, biliary tree, intestines, vas deferens, and sweat and pancreatic ducts. As a result, involvement of these organs constitutes the phenotype of CF. Infection and inflammation of the airways accounts for the majority of morbidity and mortality. The lungs become colonized with Haemophilus influenzae, Staphylococcus aureus and, later, Pseudomonas aeruginosa; less frequently the lungs become colonized with Burkholderia cepacia. These bacteria can cause an intense inflammatory response that ultimately leads to progressive damage to the airway walls and obstruction. Patients with CF suffer from recurrent pulmonary exacerbations, and are at an increased risk for spontaneous pneumothorax and hemoptysis. The upper respiratory tract is also involved, with nearly 100% of patients having radiographic evidence of pansinusitis, although in most cases they are asymptomatic. Ten per cent to 30% of patients have nasal polyps. Pancreatic insufficiency ultimately results in malabsorption of fat and protein in 90% of patients, leading to failure to thrive. Many neonates (10% to 20%) will present with meconium ileus at birth. Older children can develop partial small bowel obstructions secondary to accumulation of solid stool (distal intestinal obstruction syndrome). Some patients may develop hepatobiliary disease. Almost all males are infertile secondary to obstructive azospermia and females have decreased fertility due to thick cervical mucus. The diagnosis of CF is made on the basis of one or more characteristic phenotypic features in combination with a positive sweat chloride test on two or more occasions, or identification of two CF mutations. In this case, the patient had a history of recurrent wheezing, and a suggestion of fat malabsorption with pale, bulky stools and slow weight gain. His sweat chloride was elevated and he was ultimately found to have two CF mutations (delta F508/R1162X). A positive sweat chloride test is based on the fact that the sweat glands of patients with CF produce sweat that is abnormally high in sodium and chloride. Ninety-eight per cent of patients with CF have a sweat chloride level greater than 60 mmol/L. A minimum of 100 mg of sweat should be collected to obtain accurate test results. False positives can occur in children with hypothyroidism, Addison's disease, ectodermal dysplasia, glycogen storage disorders and nephrogenic diabetes insipidus. False negatives occur occasionally and can be caused by edema, malnutrition and an inadequate sweat collection. At least 800 different mutations have been described in the CFTR gene. Two mutations must be detected to make the diagnosis. Delta F508 is the most common mutation of CF, accounting for 70% to 80% of the mutations. Most laboratories will only test for the more common mutations. Thus, a negative genetic test does not necessarily exclude a diagnosis of CF. Children who present with recurrent wheezing in combination with failure to thrive or symptoms of malabsorption must be investigated for CF. A sweat chloride test should be the first diagnostic investigation for CF. The case presentation should not exceed 200 words and should give the reader enough information to suspect the diagnosis without making it obvious. The discussion should not exceed 600 words and should be followed by a couple of ‘clinical pearls’. A maximum of two references may be included, if helpful. The submitted cases will undergo peer review and revision at the discretion of the editors. Priority is given to cases illustrating an approach to common problems or important clinical clues to less common diagnoses that should not be missed. The Editorial Board hopes that this provides an opportunity for trainees and paediatricians practising outside of the teaching hospitals to share their clinical experiences and to publish in Paediatrics & Child Health. If you have a case to submit, contact Dr Friedman by e-mail at jeremy.friedman@sickkids.ca.

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