We evaluated the reliability of patient history and the effect of psyl
lium on symptoms and colorectal function in 12 patients with Parkinson
's disease (PD) and constipation. In all but two, constipation anteced
ed the development of parkinsonian symptoms. A comparison with prospec
tively obtained stool diaries confirmed the patients' reported constip
ation in 7 of the 12 patients. Those patients with confirmed constipat
ion had lower stool weights and reported more straining at stool. Meas
ures of colonic and anorectal function were similar in those who were
truly constipated and those who were not. Among those PD subjects with
confirmed constipation, psyllium increased stool frequency and weight
but did not alter colonic transit or anorectal function. We conclude
that prospectively obtained stool diaries should be employed to confir
m constipation in PD and that psyllium produces both subjective and ob
jective improvements in constipation related to PD.