Spasmus nutans syndrome (SNS) is a type of acquired nystagmus that usually develops within the first 2 years of life. It is clinically characterized by the following triad.
Classification-wise, it is included in congenital nystagmus in a broad sense and begins to appear from early infancy to around 3 years of age. Most cases are idiopathic benign conditions that resolve spontaneously within 2 to 3 years 1). Studies of monozygotic twins suggest familial factors.
However, approximately 15% of cases have been reported to be associated with optic nerve glioma, making imaging studies essential for exclusion 1). Rarely, it is also associated with retinal dystrophies such as congenital stationary night blindness (CSNB).
The prognosis is generally very good, and long-term follow-up studies indicate that good visual acuity can be expected. However, subclinical nystagmus may persist until 5 to 12 years of age, and there is a high incidence of refractive errors, strabismus, and developmental delays that can cause amblyopia, so careful clinical monitoring is necessary. Reports on long-term prognosis have noted that some cases have poor visual acuity or insufficient stereopsis due to complications such as esotropia, alternating hypertropia, and amblyopia, and that even when nystagmus appears to have resolved macroscopically, small-amplitude residual nystagmus may remain.
Infantile spasms occur in infants, and affected children rarely report subjective symptoms. In many cases, caregivers notice the following symptoms and seek medical attention.
The findings that constitute the triad of infantile spasms are shown below.
Nystagmus
High frequency, small amplitude: Fine eye movements described as “shimmering”
Disconjugate: Asynchronous oscillations with different amplitude and direction in each eye, often pendular.
Multidirectional: Includes horizontal, vertical, and torsional components, varying with gaze direction.
Intermittent: May be monocular, asymmetric, or intermittent. Worsens with fixation or near effort.
Head Nodding
Head nodding: Irregular low frequency (2–3 Hz) with horizontal, vertical, and torsional components.
Compensatory mechanism: Thought to be a compensatory mechanism to control nystagmus.
Torticollis
Abnormal head posture: Often head turn or torticollis.
Compensatory mechanism: Occurs as compensation for nystagmus, similar to head shaking.
Other important findings are shown below.
Fine shaking of the eyeballs, small nodding of the head, and tilting of the neck are the main signs. Pallor or edema of the optic disc and RAPD are warning signs that require urgent brain MRI referral.
Most cases of spasmus nutans are idiopathic (unknown cause) and benign. Studies of monozygotic twins suggest a genetic predisposition, but no specific gene locus has been identified.
Rarely, nystagmus resembling spasmus nutans can occur in association with the following conditions:
The diagnosis of spasmus nutans is made clinically. The triad (nystagmus, head nodding, and torticollis) can be diagnosed if confirmed during examination1). However, tests to rule out intracranial lesions or retinal dystrophy are important.
Since there is overlap between spasmus nutans syndrome and retinal diseases, it is essential to exclude retinal disease before confirming the diagnosis of spasmus nutans syndrome 1).
The main differential diagnoses are shown in the table below.
| Differential category | Main diseases |
|---|---|
| SN-like nystagmus | Optic nerve hypoplasia, achromatopsia, congenital stationary night blindness, Bardet-Biedl syndrome, hypomyelinating leukodystrophy |
| Neurological diseases | Optic pathway glioma, arachnoid cyst, opsoclonus-myoclonus syndrome, diencephalic syndrome |
| Others | Idiopathic infantile nystagmus, nystagmus blockage syndrome |
Differentiation from idiopathic infantile nystagmus: Congenital nystagmus persists throughout life, whereas in spasmus nutans, symptoms including nystagmus resolve spontaneously over several years.
Nystagmus blockage syndrome: A condition in which a patient with nystagmus adducts one or both eyes to reduce the nystagmus, resulting in esotropia. It is characterized by mild miosis during convergence and adduction of the fixating eye.
Studies have shown that the presence of intracranial lesions cannot be determined by clinical findings alone, and differentiation based on imaging is necessary.
Head nodding spasms are usually a self-limited disease and do not require specific drug therapy or surgery 1). The basics of management are as follows:
The following are known general treatments for congenital nystagmus. Although nodding spasm itself usually resolves spontaneously and is not treated, this information may be useful in cases complicated by amblyopia or refractive error.
Spasmus nutans itself resolves spontaneously, so specific treatment is usually unnecessary. However, appropriate management is required for complications such as refractive error, strabismus, and amblyopia, and regular ophthalmologic follow-up is recommended.
The exact pathogenesis of spasmus nutans remains unknown.
Head nodding and torticollis are considered compensatory mechanisms that reduce the frequency and asymmetry of nystagmus and improve vision. It is suggested that repetitive head movements or abnormal neck postures may help stabilize retinal images in response to nystagmus.
Regarding the localization of the lesion, involvement of the retina or optic nerve is suspected1). Although most cases are idiopathic, when caused by optic chiasm glioma, visual pathway damage leads to nystagmus1).
As a general feature of congenital nystagmus, it has been reported that approximately 80% of cases show a reduction or disappearance of nystagmus amplitude with convergence. This finding provides the theoretical basis for the vergence prism method mentioned earlier.
Ramanzini et al. (2024) reported a case of a 3-year-old boy presenting with nystagmus, global developmental delay, and diffuse hypomyelination on MRI 2). Initially, Pelizaeus-Merzbacher disease (PMD) was suspected, but no pathogenic mutation was found in the PLP1 gene; exome analysis identified a homozygous mutation in the GJC2 gene, leading to a diagnosis of Pelizaeus-Merzbacher-like disease (PMLD). Findings of hypomyelination in the brainstem and cerebellum, along with normal auditory brainstem responses, are clues for differentiating from PMD. In infants with nystagmus and developmental delay, hypomyelinating leukodystrophy should be included in the differential diagnosis.
Doya et al. (2022) reported a case of a 1.5-year-old girl presenting with excessive head bobbing for 3 months 3). Head bobbing worsened with walking, emotion, and stress, decreased with concentration, and disappeared during sleep. Head MRI revealed a suprasellar arachnoid cyst (3×5×7 cm) obstructing the foramen of Monro and hydrocephalus. Neuroendoscopic cyst ventriculostomy and cyst cisternostomy were performed, and head bobbing completely disappeared 6 months postoperatively. In infants with head bobbing, it is important to consider Bobble-head doll syndrome in the differential diagnosis; early imaging and surgical intervention lead to favorable outcomes.
