====== Spasmus Nutans ======

==== Definition ====

Spasmus nutans (SN) is a **rare, self-limiting paroxysmal disorder of infancy** classically defined by a clinical triad:

  * **Nystagmus** — asymmetric, disconjugate, horizontal, pendular, small-amplitude and high-frequency (up to 15 Hz); may be monocular or, occasionally, bilateral or vertical (Bonnet et al., //Movement Disorders//, 2010).
  * **Head nodding** — slow head tremor, usually "no-no" type (also "yes-yes" or rotatory), 2–3 Hz, variable amplitude, absent during sleep and thought to be compensatory for the nystagmus (Bonnet et al., //Movement Disorders//, 2010; Bellini et al., //Neurology//, 2022).
  * **Torticollis / anomalous head position** — head tilt present in ~40% of cases (Bonnet et al., //Movement Disorders//, 2010).

**Onset** is typically between 4 and 18 months (occasionally up to 3 years). It usually resolves within 1–2 years of onset, though subclinical fine nystagmus may persist to 5–12 years of age (Bonnet et al., //Movement Disorders//, 2010; Gottlob et al., //IOVS//, 1995). Prevalence among children with asymmetric congenital nystagmus is ~2.5%, with no gender difference (Bonnet et al., //Movement Disorders//, 2010).

==== Etiology / Pathogenesis ====

  * The **etiology is unclear**. Ocular motor control is thought to be transiently unstable and "plastic" in the early postnatal period; temporary disruption of afferent visual input in the first months of life may transiently affect motor control mechanisms (Bonnet et al., //Movement Disorders//, 2010).
  * **Head nodding and head tilt appear compensatory** for the nystagmus on electronystagmographic recordings (Bonnet et al., //Movement Disorders//, 2010).
  * **Familial forms** have been reported, suggesting a genetic contribution; SN may be more frequent in African-American and Hispanic families and in those of low socioeconomic status. Associations with low gestational age and low birth weight have also been described (Bonnet et al., //Movement Disorders//, 2010).

==== Evaluation ====

SN is a **diagnosis of exclusion** made only after normal clinical, ophthalmologic, electrophysiologic, and neuroimaging studies (Bonnet et al., //Movement Disorders//, 2010).

**Recommended workup:**

  * **Complete neurologic examination** — should be normal.
  * **Ophthalmologic examination including fundoscopy** — to exclude macular/optic nerve hypoplasia and retinal disease; assess for strabismus, amblyopia, and refractive error (Bellini et al., //Neurology//, 2022; Young et al., //Ophthalmology//, 1997).
  * **Brain (and orbital) MRI** — to exclude SN-like structural lesions. Eye/head movement recordings **cannot** distinguish benign SN from SN-like disease with CNS lesions; this differentiation rests on neuroimaging (Gottlob et al., //Ophthalmology//, 1990).
  * **Visual-evoked potentials and electroretinography** — normal in benign SN; useful to exclude retinal disorders (Bonnet et al., //Movement Disorders//, 2010).

**Note on neuroimaging yield:** Historically SN was associated with optic pathway gliomas (OPG), but the largest MRI series (n=40) found **no OPG and no intracranial or orbital masses**; in children with isolated SN and no other neurologic findings, neuroimaging may not always be required, though MRI remains standard to confirm the diagnosis (Bowen et al., //Journal of AAPOS//, 2017; Bellini et al., //Neurology//, 2022).

====Differential diagnosis====

  * Congenital idiopathic nystagmus (persists throughout life)
  * Opsoclonus-myoclonus syndrome
  * Bobble-head doll syndrome
  * **Secondary "SN-like" syndromes** — refractive errors, optic nerve/chiasmal gliomas, retinal disorders, cerebellar vermian hypoplasia, brain tumors, Pelizaeus-Merzbacher disease, Leigh encephalomyelopathy (Bonnet et al., //Movement Disorders//, 2010; Gottlob et al., //Ophthalmology//, 1990).

==== Management ====

  * **No pharmacologic treatment is necessary** — SN is benign and self-limiting (Bonnet et al., //Movement Disorders//, 2010).
  * **Reassurance** of the family regarding the benign natural history once serious mimics are excluded (Aung et al., //Ann Acad Med Singapore//, 1996).
  * **Ongoing monitoring** to confirm that SN remains isolated and gradually resolves; watch for emergence of neurologic or ophthalmologic abnormalities that would suggest a secondary cause (Bonnet et al., //Movement Disorders//, 2010).
  * **Detect and treat associated visual sequelae** — strabismus, amblyopia, and refractive errors are common (strabismus in 10/18 and amblyopia in 8/18 in one series); early spectacle correction and amblyopia therapy optimize visual outcomes (Young et al., //Ophthalmology//, 1997).
  * **Prognosis** — good visual acuity is the rule and psychomotor development is usually normal, though rare cases with developmental delay have been reported; subclinical nystagmus may persist for years (Bonnet et al., //Movement Disorders//, 2010; Gottlob et al., //IOVS//, 1995).

==== References ====

  - [[https://pubmed.ncbi.nlm.nih.gov/36288994/|Bellini T, et al. Teaching Video NeuroImage: Spasmus Nutans, an Infantile Nystagmus. Neurology. 2022.]]
  - [[https://pubmed.ncbi.nlm.nih.gov/20669318/|Bonnet C, et al. Developmental and benign movement disorders in childhood. Mov Disord. 2010.]]
  - [[https://pubmed.ncbi.nlm.nih.gov/8893938/|Aung T, et al. Spasmus Nutans. Ann Acad Med Singapore. 1996.]]
  - [[https://pubmed.ncbi.nlm.nih.gov/28284856/|Bowen M, et al. MRI Findings in Children With Spasmus Nutans. J AAPOS. 2017.]]
  - [[https://pubmed.ncbi.nlm.nih.gov/7499100/|Gottlob I, et al. Spasmus Nutans: A Long-Term Follow-Up. Invest Ophthalmol Vis Sci. 1995.]]
  - [[https://pubmed.ncbi.nlm.nih.gov/2234849/|Gottlob I, et al. Signs Distinguishing Spasmus Nutans From Infantile Nystagmus. Ophthalmology. 1990.]]
  - [[https://pubmed.ncbi.nlm.nih.gov/9022113/|Young TL, et al. Strabismus, Amblyopia, and Refractive Errors in Spasmus Nutans. Ophthalmology. 1997.]]