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How not to miss .... cystic fibrosis

Although CF screening started last year, those born before then may be undiagnosed and screening is not infallible. Dr Jim Littlewood explains what to look out for

Although CF screening started last year, those born before then may be undiagnosed and screening is not infallible. Dr Jim Littlewood explains what to look out for

Worst outcomes if missed

• Death in early infancy from recurrent pneumonia and malnutrition.

• Irreversible lung damage due to suboptimal treatment of chest infections before the diagnosis is considered and treatment started.

• Delayed treatment of intestinal malabsorption leading to poor early weight gain and malnutrition, permanently damaging long-term growth and overall clinical condition.

• Failure to identify CF in an infant with chronic symptoms will result in a serious loss of confidence in the medical profession on the part of the parents – and can result in medicolegal action.

Epidemiology

One in 25 of the UK population is a carrier of a CF mutation and one in 2,500 to one in 3,000 infants born in the UK have the condition.

The CF gene – on chromosome 7 – codes for cystic fibrosis transmembrane regulator (CFTR), which is involved with the transfer of chloride, sodium and water across cell membranes and controls hydration of the secretions in the airways, pancreas and liver. Disturbance of salt and water content of the secretions increases their viscosity, leading to tissue damage and – in the lungs – difficulty in eradicating infections.

Healthy carriers of the CF gene can be identified by searching for CF mutations in DNA obtained from buccal or blood specimens – particularly among blood relatives of people with CF intending to have further children by so-called ‘cascade screening'. If both parents are identified as carriers of a CF gene, antenatal diagnosis can be performed by chorionic biopsy at about three months.

Although the phenotype-genotype correlation is not close, there are a few so-called ‘mild' mutations that are more likely to be associated with some residual pancreatic function and may present in later childhood or even adult life. Furthermore, some are associated with congenital bilateral absence of the vas deferens and male infertility.

Symptoms and signs

41208971Infants with CF born in the UK are identified by newborn screening and the diagnosis is established within the first month or so. But a few may be missed by screening, so any suspicion that an infant may have CF should be confirmed or refuted, even when the newborn screening test was negative.

Some 15% of infants present in the newborn period with meconium ileus – intestinal obstruction caused by viscid intestinal secretions.

Many first develop recurrent chest infections usually starting with a cold, often with considerable wheezing in infants caused by airway obstruction. This gives a similar picture to bronchiolitis but the infections are slow to clear and are recurrent.

In others, poor weight gain – even with a reasonable energy intake – and abnormal, offensive stools that may even contain oil, is virtually diagnostic of pancreatic insufficiency.

Other modes of presentation include prolonged neonatal jaundice or later chronic liver disease, unexplained abdominal distension, rectal prolapse, nasal polyposis, male infertility, recurrent pancreatitis and heat prostration caused by excessive salt loss through sweating.

Differential diagnosis

• Recurrent chest infections are relatively common in children but most usually clear completely between episodes. Although most are unexplained, there may be an associated immunological deficiency or other structural abnormality such as an area of bronchiectasis or even ciliary dyskinesia. An inhaled foreign body such as a peanut may also cause recurrent infections and may only be identified later at bronchoscopy.

• Oesophageal reflux with chronic episodes of inhalation or even a tracheo-oesophageal fistula.

• Asthma may present with similar signs and symptoms – CF is best excluded if the asthma appears typical and is associated with allergic problems.

• Chronic bowel symptoms, usually diarrhoea, may relate to food intolerance, chronic infections or even coeliac disease. Sometimes chronic constipation is the main symptom of CF. Abdominal distension is common in many GI disorders and can be caused by benign conditions such as air swallowing or more serious causes such as CF or coeliac disease.

First-line investigations

• A sweat test performed by laboratory personnel experienced in the technique – repeated if positive or equivocal.

• Respiratory culture (T/S, cough swab

or bronchoalveolar lavage) may show Staphylococcus aureus or Pseudomonas aeruginosa.

• Respiratory function tests in children over five years.

• Chest X-ray may show hyperinflation and infection.

• Faecal fat – microscopy or estimation of total fat.

• Faecal pancreatic elastase – very low in the 90% of pancreatic insufficient infants after the first two weeks.

• Screening for the CF mutations known to be most frequent in the local population.

Second-line investigations

• FBC, immunoglobulins, LFTs, liver ultrasound.

• Fat soluble vitamin levels.

• Semen analysis (in selected males).

41208972Delayed diagnosis until after severe chest damage has occurred should now be a rare occurrence. But if the diagnosis is suggested or seems even a remote possibility, it cannot be emphasised too strongly that CF should be excluded at least by a sweat test even if the infant or child has been screened. It is also worth remembering that in some areas of the UK neonatal CF screening only started in 2007. So any infant or child who has recurrent or chronic chest and bowel symptoms or signs should have a sweat test performed.

Dr Jim Littlewood is chair of the Cystic Fibrosis Trust and former director of the Regional Paediatric CF Clinic at St James's University Hospital in Leeds

questions herrings CT slice through the chest of a CF patient, showing bronchioles filled with mucus (in red) CT slice through the chest of a CF patient, showing bronchioles filled with mucus (in red)

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