• sarcoidosis
• paediatric interstitial lung disease

The finding of granulomas on paediatric tissue biopsy is non-specific, with a wide differential diagnosis that includes chronic infection (eg, tuberculous, atypical Mycobacterium infection, leprosy, Lyme disease, brucellosis, syphilis and histoplasmosis), immunodeficiency (hyper-IgM syndrome, chronic granulomatous disease), connective tissue disease (juvenile chronic arthritis) and miscellaneous conditions such as Blau’s syndrome, Melkersson-Rosenthal syndrome, Anderson-Fabry disease and Vogt-Koyanagi-Harada syndrome. Tumours such as hepatoblastoma and neuroblastoma may also provoke a granulomatous reaction.1 Another important differential is sarcoidosis which, like many of the above, is rare in children and has a wide clinical spectrum of severity. Older children with sarcoidosis usually have a presentation similar to adults, with frequent hilar lymphadenopathy and pulmonary infiltrates. Early-onset sarcoidosis, usually presenting before the age of four, is more frequently characterised by uveitis, rash and arthritis2 and one could question whether the two diseases are really the same entity.

Unlike some of the other conditions associated with granulomas, there is no specific diagnostic test for sarcoidosis. An elevated serum ACE is supportive but non-specific and there are cases diagnosed as sarcoidosis with no serum abnormality. Given that there is no gold-standard diagnosis test for sarcoidosis, and that sarcoidosis is likely an umbrella term under which lurk several different disease entities, how can we hope to make progress towards finding a specific cause, when the first prerequisite towards achieving this is to assemble a large cohort? Even …