Expression of neuropeptides in normal and abnormal appendices

Abstract

Background/purpose: Increased neuroproliferation in the appendix associated with an increase in substance P (SP), vasoactive intestinal polypeptide (VIP), and growth-associated protein-43 (GAP-43) has been documented in appendices of adults with acute right lower quadrant (RLQ) abdominal pain and absence of gross or histologic signs of appendiceal inflammation. The authors tested whether these findings were present in children with RLQ pain and a normal appendix.

Methods: Immunohistochemistry staining of paraffin-embedded appendices was performed with GAP-43, VIP, and SP. The positive control group included appendices with acute inflammation (group I, n = 5); the negative control group included appendices removed incidentally (group II, n = 5); and the experimental group included appendices from children suspected to have acute appendicitis without histologic signs of inflammation (group III, n = 9).

Results: Group I: VIP was strongly expressed in the nerve plexuses. The lamina propria and muscularis showed absent or minimal VIP expression. SP staining was strong in all plexuses and was moderate to strong in the muscularis. SP expression in the epithelium and lamina propria was difficult to quantify secondary to inflammation. Group II: VIP expression was essentially undetectable in the epithelium, lamina propria, and muscularis, and was moderate in the nerve plexuses. Mild SP staining was detected in the nerve plexuses of most specimens, and absent to mild staining was found in the epithelium and muscularis. However, one specimen strongly expressed SP in all layers. Group III: VIP expression was moderate to strong in the lamina propria and muscularis of nearly all specimens, and strong expression was found in all nerve plexuses. All but one specimen strongly expressed SP in plexuses. There was moderate to strong expression of SP in the epithelium, lamina propria, and muscularis in over 50% of specimens. The immunostaining for GAP-43 was very weak and nonspecific and did not help discriminate between the 3 study groups.

Conclusions: Increased neuroproliferation in the lamina propria and muscularis was evident in patients with abdominal pain and normal appendices compared with appendices removed incidentally. The VIP and SP expression in these patients was similar or higher than that observed in patients with acute inflammation on histology.