Rarity and review: evidence-based practice for uncommon diseases

Excerpt

Practice recommendations based on solid evidence are often difficult to obtain for relatively common conditions. The challenge is even greater for rare diseases. For example, carcinoid is an uncommon tumour arising from the enterochromaffin cells of the gut. Grouped with other hormone-producing tumours, such as insulinoma, glucagonoma, gastrinoma, VIPoma (for vasoactive intestinal peptide), carcinoid and neuroendocrine tumours have a combined incidence of 5.2 per 100,000 population, with approximately half being carcinoid.1 Several classification systems attempt to describe these diverse diseases,2,3 although discussions restricted to carcinoid tumours often focus on the embryological origin of the parent tissue: foregut (thymus, esophagus, lung, stomach, duodenum, pancreas), midgut (appendix, ileum, cecum, ascending colon), and hindgut (distal large bowel, rectum).4 Carcinoid tumours are capable of secreting a variety of vasoactive substances, including serotonin, histamine, and kinin peptides, although only 25% do this,5 and only 10% result in carcinoid syndrome.6 Characterized by flushing, diarrhea, abdominal pain, and bronchoconstriction, carcinoid syndrome occurs when the tumour’s metabolic products escape hepatic metabolism by either metastasis or primary locations outside the portal circulation.6 Octreotide, a somatostatin analogue that inhibits secretion of hormones in functioning neuroendocrine tumours, reduces symptoms among those suffering from carcinoid syndrome. A life-threatening carcinoid crisis characterized by hemodynamic instability, arrhythmias, bronchospasm, and coma7 may result when tumours are physically or chemically stimulated to release massive quantities of vasoactive substances. The management of this latter condition is the focus of a systematic review in this issue of the Journal. …