No relationship between vasoactive intestinal polypeptide expression and headache in pituitary tumours

Clinical studies have noted the common presentation of pituitary tumours with significant headache. This has been considered to be one, or a combination of, increased cranial pressure, tumour size with dural stretch, or cavernous sinus invasion. Newer hypotheses suggest an association between the presence of pituitary tumour-associated headaches and the expression and release of nociceptive substances. Vasoactive intestinal polypeptide (VIP), a marker of the cranial parasympathetic system, is increased during acute attacks of some primary headaches, and with its expression in the pituitary may link some pituitary tumours to their headache presentations.

Using immunohistochemical techniques, VIP expression in pituitary tumour specimens was examined to determine if there was a relationship between the presence or absence of pituitary-associated headache and the expression of VIP immunoreactivity (VIP-IR). A qualitative analysis of the VIP-IR in pituitary cells was performed by observers blinded to the headache status of each patient. The presence of VIP-IR and headache were treated as binary variables and associations tested with chi-square tests.

Forty-five per cent of specimens positive for VIP were from patients presenting with headache. There was no statistically significant association between the presence of VIP-IR and headache (chi(2) = 0.077, P = 0.781).

Although the significance of VIP positivity in pituitary tumour-associated headache is unknown it seems unrelated to headache. It remains possible that the mechanism of these headaches relates to the production of either an as yet unidentified peptide, or a combination of nociceptive peptides.