Primary ciliary dyskinesia — formative SAQs

SAQ 1 — The preschooler with a lifelong wet cough and situs inversus (20 marks, ~15 minutes)

A 4-year-old girl is referred with a wet cough that her parents say has been present on most days since she was a few weeks old. She had unexplained respiratory distress as a term newborn, has a constantly runny nose, and has had recurrent glue ear with two sets of grommets. A chest radiograph incidentally shows the heart on the right side. ^[4]

Questions

1. Give the most likely diagnosis and the features in this history that support it. (6 marks) ^[4]
2. Name the single most important alternative diagnosis to exclude and how you would exclude it. (4 marks) ^[2]
3. Outline the diagnostic pathway you would use to confirm the diagnosis. (6 marks) ^[1]
4. Explain why a normal chest radiograph and normal organ position would not exclude the diagnosis in another child. (4 marks) ^[4]

Model answer (must-hit)

1. The most likely diagnosis is primary ciliary dyskinesia, in this child specifically Kartagener syndrome because situs inversus is present. Supporting features are the daily wet cough present since the first weeks of life, unexplained neonatal respiratory distress in a term infant, chronic year-round rhinorrhoea, recurrent otitis media with effusion needing grommets, and dextrocardia indicating situs inversus. ^[4]
2. The single most important alternative to exclude is cystic fibrosis, because it is the other leading genetic cause of early-onset wet cough and bronchiectasis. It is excluded with a sweat chloride test and, where indicated, cystic fibrosis genetic testing, remembering to also assess for pancreatic insufficiency and faltering growth. ^[2]
3. The diagnostic pathway is performed in a specialist centre and combines tests because none is sufficient alone: nasal nitric oxide as a screen (characteristically very low), high-speed video microscopy of a nasal brushing to assess ciliary beat frequency and pattern, transmission electron microscopy for ultrastructural defects such as absent dynein arms, and genetic panel testing, with immunofluorescence as an adjunct. ^[1]
4. Normal organ position does not exclude PCD because the laterality defect is present in only about half of affected children; the other half have normal situs and identical airway disease. The diagnosis therefore rests on the clinical phenotype and the specialist diagnostic tests rather than on organ position. ^[4]