Duane syndrome


Duane syndrome is a congenital rare type of strabismus most commonly characterized by the inability of the eye to move outward. The syndrome was first described by ophthalmologists Jakob Stilling and Siegmund Türk, and subsequently named after Alexander Duane, who discussed the disorder in more detail in 1905.
Other names for this condition include: Duane's retraction syndrome, eye retraction syndrome, retraction syndrome, congenital retraction syndrome and Stilling-Türk-Duane syndrome.

Presentation

The characteristic features of the syndrome are:
While usually isolated to the eye abnormalities, Duane syndrome can be associated with other problems including cervical spine abnormalities Klippel–Feil syndrome, Goldenhar syndrome, heterochromia, and congenital deafness.

Causes

Duane syndrome is most probably a miswiring of the eye muscles, causing some eye muscles to contract when they shouldn't and other eye muscles not to contract when they should. Alexandrakis and Saunders found that in most cases the abducens nucleus and nerve are absent or hypoplastic, and the lateral rectus muscle is innervated by a branch of the oculomotor nerve. This view is supported by the earlier work of Hotchkiss et al. who reported on the autopsy findings of two patients with Duane's syndrome. In both cases the sixth cranial nerve nucleus and nerve was absent, and the lateral rectus muscle was innervated by the inferior division of the third or oculomotor nerve. This misdirection of nerve fibres results in opposing muscles being innervated by the same nerve. Thus, on attempted abduction, stimulation of the lateral rectus via the oculomotor nerve will be accompanied by stimulation of the opposing medial rectus via the same nerve; a muscle which works to adduct the eye. Thus, co-contraction of the muscles takes place, limiting the amount of movement achievable and also resulting in retraction of the eye into the socket. They also noticed mechanical factors and considered them secondary to loss of innervation: During corrective surgery fibrous attachments have been found connecting the horizontal recti and the orbital walls and fibrosis of the lateral rectus has been confirmed by biopsy. This fibrosis can result in the lateral rectus being 'tight' and acting as a tether or leash. Co-contraction of the medial and lateral recti allows the globe to slip up or down under the tight lateral rectus producing the up and down shoots characteristic of the condition.

Genetics

There are two known genetic associations with Duane Syndrome In some families the condition is associated with variants in the CHN1 gene and in others it is associated with variants in the MAFB gene.

Diagnosis

Classification

Duane's syndrome has three variants:
Brown has classified Duane's syndrome according to the characteristics of the limitation of movement-
The first type is more common and accounts for 85% of the cases.

Differential diagnosis

In the clinical setting, the principal difficulties in differential diagnosis arise as a consequence of the very early age at which patients with this condition first present. The clinician must be persistent in examining abduction and adduction, and in looking for any associated palpebral fissure changes or head postures, when attempting to determine whether what often presents as a common childhood squint is in fact Duane syndrome. Fissure changes, and the other associated characteristics of Duane's such as up or down shoots and globe retraction, are also vital when deciding whether any abduction limitation is the result of Duane's and not a consequence of VI or abducens cranial nerve palsy.
Acquired Duane's syndrome is a rare event occurring after peripheral nerve palsy.

Treatment

The majority of patients remain symptom free and able to maintain binocularity with only a slight face turn. Amblyopia is uncommon and, where present, rarely dense. This can be treated with occlusion, and any refractive error can also be corrected.
Duane syndrome cannot be cured, as the "missing" cranial nerve cannot be replaced, and traditionally there has been no expectation that surgery will result in any increase in the range of eye movement. Surgical intervention, therefore, has only been recommended where the patient is unable to maintain binocularity, where they are experiencing symptoms, or where they are forced to adopt a cosmetically unsightly or uncomfortable head posture in order to maintain binocularity. The aims of surgery are to place the eye in a more central position and, thus, place the field of binocularity more centrally also, and to overcome or reduce the need for the adoption of an abnormal head posture. Occasionally, surgery is not needed during childhood, but becomes appropriate later in life, as head position changes.
Surgical approaches include:
Most patients are diagnosed by the age of 10 years and Duane's is more common in girls than boys. A French study reports that this syndrome accounts for 1.9% of the population of strabismic patients, 53.5% of patients are female, is unilateral in 78% of cases, and the left eye is affected more frequently than the right. Around 10–20% of cases are familial; these are more likely to be bilateral than non-familial Duane syndrome. Duane syndrome has no particular race predilection.