RESUMO
Chronic intestinal pseudo-obstruction (CIPO), a rare, debilitating disorder of bowel motility dysfunction, is largely a clinical diagnosis, without any universally accepted diagnostic criteria. Three subgroups are generally acknowledged based on the cell-type affected: enteric visceral myopathy (the most common subgroup), neuropathy, and mesenchymopathy. A fourth subgroup includes abnormalities of neurohormonal peptides. Although immunohistochemical staining is reportedly useful for identifying the mesenchymopathic type, its role in diagnosing enteric visceral myopathy and neuropathy has been fraught with difficulties. We present two cases of chronic intestinal pseudo-obstruction that are clinically and histopathologically suggestive of type III visceral enteric myopathy, aiming to expound upon the diagnostic and pathogenic features. We found that the outer-longitudinal layer of the muscularis propria was more severely affected as compared with the inner circular layer. To investigate the value of this finding, we performed immunostains in the one case in which a paraffin block was available. We found increased peripherin and calretinin immunopositive nerve fibers in the outer layer as compared with inner, but without any significant increase in S-100 positivity or alteration in neuronal morphology of myenteric plexus, a novel finding. This differential staining pattern was completely different from Hirschsprung disease, in which we found rare to absent peripherin and calretinin staining. It is unclear if this increase in the outer layer in visceral myopathy reflects a reactive change or dysfunctional axons. In addition, the history of volvulus in one patient and transmural inflammatory changes in the second raise concerns about the higher propensity of clinical complications secondary to the attenuated outer muscular layer. This study suggests that enteric visceral myopathy has histologic and staining characteristics different from Hirschsprung disease, a finding of diagnostic significance in the differential diagnosis of bowel obstruction. Moreover, these features may have pathogenic value and need further confirmation.