Little progress has been made in finding the cause of LCH. Epidemiolog
ic studies are difficult because of the rarity of the disease. Althoug
h several associations have been demonstrated in case-control studies-
in particular the association with thyroid disease-no causal relations
hips have been documented. Additional case-control studies may uncover
the to-date missing lead that proves fruitful for epidemiologic inves
tigation.