Structural basis of voiding dysfunction in megacystis microcolon intestinal hypoperistalsis syndrome

Megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) is a rare, congenital and usually fatal condition of unknown etiology. It is characterized by abdominal distension caused by a distended, non-obstructed urinary bladder and intestinal hypoperistalsis with functional intestinal obstruction. Previous studies reported vacuolar degenerative changes in the smooth muscle cells of bowel and bladder suggesting that MMIHS may be due to a visceral myopathy. The aim of this study was to examine the expression of contractile, cytoskeletal and extracellular matrix proteins in the detrusor muscle of MMIHS patients.

Bladder specimens were obtained from six MMIHS patients. Normal bladder specimens were obtained during partial cystectomy and served as controls. Single fluorescence immunohistochemistry for alpha-smooth muscle actin (SMA), desmin, dystrophin, vinculin and collagen types I and III was carried out. Specific connective tissue stains (trichrome Masson, van Gieson) and electron microscopical investigations were also performed.

Trichrome Masson and van Gieson staining demonstrated markedly increased dense connective tissue between the layers of the detrusor muscle in MMIHS compared to controls. Collagen type I immunoreactivity was markedly increased and SMA, desmin and dystrophin immunoreactivity was markedly reduced in the bladder muscle of MMIHS compared to controls. Electron microscopy revealed vacuolar degenerative changes in smooth muscle cells and an abundance of connective tissue between these cells.

These data suggest that the detrusor muscle in MMIHS is strikingly abnormal and is the likely cause of voiding dysfunction.