Objectives: Compared with pain-free controls, patients with fibromyalgia (FM) have more mast cells in the skin. Whether mast cells are involved in the pathogenesis of FM is unclear. We sought to determine the effects of a mast cell stabilizer (ketotifen) on FM symptoms.
Materials and methods: Fifty-one FM patients were randomized to daily oral ketotifen 2 mg bid (n=24) for 8 weeks or placebo (N=27). Mean age of patients was 51.2 years (SD=8.4); 88% were female and 88% were white; 22% were taking concomitant opiates; and mean pressure pain sensitivity (range, 0 to 20) was 10.0 (0.4). At study entry, the weekly average pain intensity was 6.4 (1.1) and the mean score on the Revised Fibromyalgia Impact Questionnaire-Revised was 66.8 (14.0).
Results: We found no statistically significant treatment group differences from baseline in either group for the 2 primary measures: weekly average pain intensity (ketotifen -1.3 [1.9] vs. placebo -1.5 [1.9], P=0.7); and Fibromyalgia Impact Questionnaire-Revised score (-12.1 [19.5] vs. -12.2 [18.1], P=0.9). No secondary outcome measures (Brief Pain Inventory pain intensity and pressure pain sensitivity) reached statistical significance; results did not differ in the intent-to-treat and completer analyses. Other than transient sedation (6 [28.6%] vs. 1 [4.0%]), ketotifen was well tolerated.
Discussion: The study results question whether skin mast cells play a major role in the pathogenesis of FM. However, given the role of mast cells in peripheral and central nociception, and the minimal side effects of ketotifen, a randomized clinical trial using increasing doses of ketotifen may be warranted.