*3.1.1 Genetic*

Bilateral abductor palsy presenting with the genetic etiology is very rare. Presentation may be with an isolated paralysis of vocal folds or as a spectrum of various clinical features. Plott syndrome, described by Plott in 1964 [2], is a rare entity demonstrating X-linked recessive inheritance. Patients usually present with bilateral vocal fold paralysis and mental retardation. Autosomal dominant mode of inheritance has also been reported [3–5]. Other syndromic associations may be Down's syndrome, Moebius syndrome, congenital myasthenic syndrome, 22q deletion syndrome and Goldenhar syndrome [6]. Rarely, it may be an isolated presentation of brainstem discontinuity, for example, medullary defect. This is a very rare congenital abnormality where there is a segmental discontinuity of brainstem [7].

#### *3.1.2 Nongenetic*

Several developmental anomalies of brain and brainstem may secondarily present with bilateral abductor palsy. Arnold Chiari malformation, congenital hydrocephalus, meningomyelocele, syringomyelia, syringobulbia, etc. are such examples.

#### **3.2 Acquired causes**

Various etiological factors have been mentioned in the literatures so far. Following are the common acquired causes for bilateral abductor palsy.
