Rare single system diseases.

There are many rare conditions to be found in textbooks of respiratory paediatrics which are often difficult to place in to any standard form of classification. The expertise of any single paediatrician or centre in the management of such problems is inevitably limited, and so treatment is never "evidence based" but depends on individual experience and information contained in case reports or small series in the literature. The investigation and management of such cases is often complex and should be performed in large regional centres. In this article we will discuss pulmonary alveolar microlithiasis, disorders of the lymphatic system, lymphoid bronchiolitis and pulmonary langerhans cell histiocytosis.