Choroideremia

At a glance

An inherited eye disorder characterized by progressive degeneration of the choroidea, retinal pigment epithelium, and neural retina.

Synonym

Progressive Tapetochoroidal Dystrophy.

Incidence

The estimated prevalence is approximately 1.5:100,000 in the general population.

Genetic inheritance

X-chromosomal recessive transmission. Almost exclusively affects men, but a few female cases have been described. The responsible gene has been mapped to chromosome Xq21.2.

Pathophysiology

A point mutation is responsible for impairment in geranyl transferase, which affects the vesicle transport in retinal cells in choroideremia.

Diagnosis

Based on the clinical findings of progressive degeneration of the choroidea, with night blindness occurring in teenage years. The differential diagnosis includes gyrate atrophy of the choroid, diffuse atrophy of the choriocapillaris, and X-linked retinitis pigmentosa. The combination of inheritance mode, ophthalmic examination, visual field testing, and electroretinography (ERG) helps to confirm the diagnosis.

Clinical aspects

Affected males usually first note symptoms in adolescence, experiencing night blindness, and peripheral visual field loss. The ERG in affected males may initially show a pattern of rod-cone degeneration. Fundoscopy reveals patchy areas of chorioretinal degeneration, usually beginning in the mid-peripheral areas of the fundus and manifesting as a ring scotoma. As these areas enlarge, the disease progresses to marked loss of the retinal pigment epithelium and the choriocapillaris, while deep choroidal vessels are preserved. Although the function and anatomy of the central macula is preserved until late in the disease process, affected men rarely retain any central vision beyond the seventh decade of life. Almost one-third of these patients also have posterior sub-capsular cataracts. Although choroideremia is essentially a retinal degenerative disease, associations with other clinical findings such as severe mental retardation, agenesis of the corpus callosum, signs of encephalopathy, (sensorineural and conductive) hearing loss, distal motor neuropathy, and cleft lip and palate have been reported. No effective treatment exists.

Precautions before anesthesia

Routine preoperative assessment is considered adequate. Check for concomitant diseases as mentioned above and, if present, they need to be evaluated with regards to anesthesia. Developmental delay, particularly in combination with decreased vision and/or impaired hearing may cause agitation and stress in the perioperative period, thus anxiolytic and sedative premedication and/or presence of a parent (or primary caregiver) for induction of anesthesia may be beneficial.

Anesthetic considerations

In the presence of peripheral motor weakness, the effects of neuromuscular blocking agents may be enhanced and careful titration to effect is recommended using a peripheral nerve stimulator. If muscle weakness is severe and involves the respiratory muscles, prolonged mechanical ventilation may be required postoperatively. The presence or absence of other neurologic findings may influence the anesthetic technique.