Electron microscopic findings in levator muscle biopsies of patients with isolated congenital or acquired ptosis

Abstract

Systemic mitochondriopathies as chronic progressive external ophthalmoplegia (CPEO) are frequently associated with ptosis. We investigated whether mitochondrial abnormalities in the levator muscle are also found in patients with isolated congenital or acquired ptosis showing no other signs of mitochondrial cytopathy. Biopsies of levator muscle were taken during surgery from 24 patients with isolated congenital (group 1) or early-onset acquired ptosis (group 2). All patients were given a thorough clinical examination before and after surgery. Ultrathin muscle sections were examined by transmission electron microscopy. The findings were compared with biopsies from five patients with CPEO (positive control) and two patients with traumatic ptosis or pseudoptosis (negative control). The mean levator function equalled 7.3 mm (range 4-10 mm) in group 1 and 12.8 mm (range 9-15 mm) in group 2. Eight out of 11 patients in group 1 and eight out of 13 patients in group 2 were found to have mitochondrial alterations such as megamitochondria, mitochondrial matrix alterations and abnormal cristae, similar to CPEO. Within group 1 and 2, no significant clinical differences were found between patients with and without mitochondrial abnormalities. Mitochondrial alterations were found in a surprisingly large proportion of levator biopsies from patients with isolated congenital or early-onset acquired ptosis. There was no statistically significant correlation between mitochondrial alterations and levator function. Our findings suggest that the ultrastructural assessment of mitochondria in the eyelid muscle is a valuable tool, and may guide further biochemical and mutation screening tests that will help to understand the etiopathology of this disease.