Deficient alpha smooth muscle actin expression as a cause of intestinal pseudo-obstruction: fact or fiction?

AIMS To test the hypothesis that deficient alpha smooth muscle actin (ASMA) expression in intestinal smooth muscle, as assessed by immunohistochemistry, is specifically associated with clinical evidence of intestinal pseudo-obstruction. METHODS Seventeen archival, formalin fixed, paraffin wax embedded samples of small intestine and 12 samples of large intestine were studied. Two of the small bowel samples and one large bowel sample were from patients with symptoms of intestinal pseudo-obstruction. The controls were longitudinal surgical margins from hemicolectomies performed for carcinoma. Immunohistochemistry was performed using primary antibodies to ASMA, smooth muscle myosin heavy chain (SMMHC), and desmin. The relative intensities of immunohistochemical expression in the circular and longitudinal muscle layers of the muscularis propria were assessed in each sample, for all three markers. RESULTS All samples showed strong SMMHC and desmin expression in the inner circular and outer longitudinal layers of the muscularis propria. Both small intestinal samples from the cases and 11 of 15 controls showed no or minimal ASMA expression in the inner circular layer, with the remaining four controls also showing ASMA labelling in this layer that was weaker than within the longitudinal muscle. In contrast, intense ASMA expression was seen in both muscle layers within the large intestine in the remaining case, and in the controls. CONCLUSIONS There is insufficient evidence from this study to support the hypothesis that ASMA deficiency in intestinal smooth muscle, as determined by immunohistochemistry on archival tissues, is specifically associated with intestinal pseudo-obstruction.