Spasmus Nutans

Spasmus nutans (SN) is a rare eye disease characterized by the clinical triad of asymmetric and pendular nystagmus, head nodding, and torticollis.

Epidemiology

The prevalence of SN is unknown.

Clinical description

The age of disease onset ranges from 4-12 months and clinically, SN is characterized by a triad of signs which are nystagmus, head nodding, and abnormal head turn or tilt (torticollis). The nystagmus in SN is typically pendular, intermittent, of small-amplitude, high frequency oscillations (shimmering nystagmus) and is usually bilateral, but it can be monocular, asymmetric, and variable in different positions of gaze. Head nodding is not always present, and often follows the onset of nystagmus. It is usually intermittent and of lower frequency than the nystagmus. Both nystagmus and head nodding can occur in any plane (horizontal (more frequent), vertical, oblique, or torsional). Strabismus and amblyopia may be present while oscillopsia is absent. Optic nerve, retinal, or intracranial abnormalities are generally absent.

Etiology

SN is an idiopathic disorder. Head nodding suppresses nystagmus through the vestibular-ocular reflex and aids vision. Similarly, the torticollis has been observed clinically and by electrooculography (EOG) recordings to dampen nystagmus by a hypothesized vestibular mechanism. Low socioeconomic status represents a risk factor for the development of SN.

Diagnostic methods

The diagnosis relies on exclusion of neurological and ophthalmological diseases. Eye movement recordings reveal a fine, high frequency, pendular horizontal nystagmus, which cannot be seen superimposed upon the normal optokinetic response. Visual acuities are generally lower in the eye with the greater nystagmus and vary between 6/6 and 6/24. Optic disc examinations are usually normal. Visual electrophysiology (visual evoked potential (VEP) and electroretinograms (ERG)) should be performed to exclude retinal diseases which can mimic SN.

Differential diagnosis

Differential diagnosis includes SN-like nystagmus, which is defined as a condition where children have nystagmus, head nodding and abnormal head position similar to SN but symptoms are associated with low vision (for example optic nerve hypoplasia, achromatopsia, congenital stationary night blindness, Bardet-Biedl syndrome), neurologic diseases (optic pathway glioma (chiasmal), arachnoid cyst, opsoclonus-myoclonus syndrome, diencephalic syndrome, and Leigh syndrome (see these terms), or systemic abnormalities. Nystagmus may also be associated with idiopathic infantile nystagmus (see this term). SN may also be misdiagnosed as thalamic neoplasm and empty sella.

Genetic counseling

SN is generally sporadic but cases of SN occurring in monozygotic twins have been reported.

Management and treatment

No cure exists and treatment is mainly supportive. This includes treatment for strabismus, amblyopia and refractive errors.

Prognosis

SN is a benign eye motility disorder where patients are usually healthy. The nystagmus has a tendency to decrease in intensity with age and symptoms tend to spontaneously remit within 1 to 5 years of onset with fine, residual nystagmus detectable only on eye movement recording. However, in rare cases, the signs may persist for as long as 8 years.