We report the results of a prospective registration of the prevalence of in
terstitial lung diseases by 20 centres of respiratory medicine in Flanders
from January 1992 till July 1996. The 20 centres registered a total of 362
cases. Sarcoidosis (31% with inclusion of stage I, or 22% without stage I),
idiopathic pulmonary fibrosis (20%), hypersensitivity pneumonitis (13%) an
d unclassified forms of interstitial lung diseases (9%) were the most often
diagnosed diseases. The mean age of the patients was 52 +/- 17 (SD) years,
but ranged from 32 +/- 10 years in histiocytosis X to 70 +/- 13 years in d
rug induced interstitial lung diseases. The male to female ratio was 1.3 bu
t ranged from 2.3 in interstitial lung diseases due to inhalation of inorga
nic materials to 0.8 in interstitial lung diseases due to connective tissue
disease. The diagnosis was considered certain in 60%, probable in 30% and
possible in 10%. In 50% of the cases the diagnosis was proven by biopsy and
the most often used biopsy technique was transbronchiolo-alveolar biopsy (
40% of biopsies) followed by open lung biopsy (32%). At diagnosis vital cap
acity was 82 +/- 22% pred. (ranging from 92 +/- 19% in sarcoidosis to 71 +/
- 24% in idiopathic pulmonary fibrosis) and GO-diffusing capacity was 77 +/
- 19% pred. (ranging from 77 +/- 19% in sarcoidosis to 41 +/- 13% in drug i
nduced pneumonitis). The regional frequency of interstitial lung diseases i
n Flanders varied widely and was not proportional to the regional distribut
ion of the 20 contributing centres. In conclusion this registration provide
s interesting information on the occurrence and presentation of the differe
nt forms of interstitial lung diseases, although it may still underestimate
the real prevalence and incidence of interstitial lung diseases.