OCULOMOTOR NERVE AND MUSCLE ABNORMALITIES IN CONGENITAL FIBROSIS OF THE EXTRAOCULAR-MUSCLES

Congenital fibrosis of the extraocular muscles is an autosomal dominan t congenital disorder characterized by bilateral ptosis, restrictive e xternal ophthalmoplegia with the eyes partially or completely fixed in an infraducted (downward) and strabismic position, and markedly limit ed and aberrant residual eye movements. It has been generally thought that these clinical abnormalities result from myopathic fibrosis of th e extraocular muscles. We describe the intracranial and orbital pathol ogy of 1 and the muscle pathology of 2 other affected members of a fam ily with chromosome 12-linked congenital fibrosis of the extraocular m uscles. There is an absence of the superior division of the oculomotor nerve and its corresponding alpha motor neurons, and abnormalities of the levator palpebrae superioris and rectus superior (the muscles inn ervated by the superior division of the oculomotor nerve). In addition , increased numbers of internal nuclei and central mitochondrial clump ing are found in other extraocular muscles, suggesting that the muscle pathology extends beyond the muscles innervated by the superior divis ion of cranial nerve III. This report presents evidence that congenita l fibrosis of the extraocular muscles results from an abnormality in t he development of the extraocular muscle lower motor neuron system.