Are nyctalopia, eye pressing, paradoxical pupils, and high refractive error specific to retinal dystrophy in spasmus nutans syndrome?

Nyctalopia, Eye Pressing, Paradoxical Pupils, and High Refractive Error in Spasmus Nutans Syndrome

These clinical features are NOT specific to spasmus nutans syndrome itself, but rather indicate underlying retinal dystrophy that can mimic or coexist with spasmus nutans—making electroretinography mandatory to distinguish true spasmus nutans from retinal disease.

Critical Diagnostic Distinction

A normal electroretinogram (ERG) is required to confirm the diagnosis of true spasmus nutans, as retinal dystrophies can simulate all the clinical findings of spasmus nutans. 1 In one study, 3 of 8 patients (38%) clinically thought to have spasmus nutans actually had abnormal ERGs indicating retinal dystrophy rather than true spasmus nutans. 1

Specific Clinical Features and Their Significance

Nyctalopia (Night Blindness)

• Nyctalopia is a hallmark symptom of retinal dystrophy, particularly rod or rod-cone dystrophy, and is NOT a feature of true spasmus nutans. 2
• When present in a child with spasmus nutans-like nystagmus, this strongly suggests underlying retinal disease requiring ERG evaluation. 2

Eye Pressing (Oculodigital Sign)

• Eye pressing behavior is characteristic of retinal dystrophies and sensory visual deficits, not idiopathic spasmus nutans. 2
• This behavior represents the child's attempt to stimulate the retina through mechanical pressure. 2

Paradoxical Pupils

• Paradoxical pupillary responses indicate afferent visual pathway dysfunction and are associated with retinal disease, not true spasmus nutans. 2
• This finding mandates ERG testing to evaluate for cone or rod-cone dystrophy. 2, 1

High Refractive Error

• High refractive errors (≥6.00 D myopia, ≥3.00 D hyperopia, or ≥3.00 D astigmatism) are common in both true spasmus nutans and retinal dystrophy cases. 3, 2, 4
• In a recent study, 85% of spasmus nutans patients with multiple exams had amblyogenic refractive errors. 4
• However, high refractive error alone does not distinguish between true spasmus nutans and retinal dystrophy. 2

Prevalence of Underlying Pathology in Spasmus Nutans-Like Presentations

A substantial proportion of patients presenting with spasmus nutans-like nystagmus have important underlying conditions:

• Only 3 of 22 patients (14%) in one series had no associated ocular, intracranial, or systemic abnormalities. 2
• Four patients (18%) had cone or rod-cone dystrophy. 2
• Two patients (9%) had chiasmal gliomas. 2
• Seven patients (32%) had strabismus. 2

Mandatory Diagnostic Algorithm

When evaluating a child with suspected spasmus nutans who exhibits nyctalopia, eye pressing, paradoxical pupils, or high refractive error:

1. Perform ERG according to international standards to distinguish true spasmus nutans from retinal dystrophy. 1
2. Obtain MRI of the brain without and with IV contrast to exclude chiasmal glioma and other intracranial pathology. 5, 2
3. Conduct comprehensive cycloplegic refraction to identify and correct amblyogenic refractive errors. 3, 4
4. Assess for strabismus and amblyopia, which occur in 56% and 44% of spasmus nutans patients respectively. 6

Critical Pitfalls to Avoid

• Do not assume a diagnosis of benign spasmus nutans based solely on clinical appearance of nystagmus, head nodding, and torticollis. 1 The presence of nyctalopia, eye pressing, or paradoxical pupils mandates ERG evaluation.
• Do not confuse spasmus nutans with retinal dystrophy-associated nystagmus, as the latter requires different management and has different visual prognosis. 2, 1
• Do not delay neuroimaging, as chiasmal gliomas can present with identical clinical features to spasmus nutans. 5, 2

Long-Term Visual Outcomes

Even in true spasmus nutans without retinal dystrophy:

• Mean best-corrected visual acuity at final exam was 0.48 LogMAR (approximately 20/60) in the better-seeing eye. 4
• Only one-third of patients achieve normal stereoacuity. 7
• Subclinical nystagmus persists until at least 5-12 years of age despite clinical resolution. 7
• Eight of 32 patients (25%) required amblyopia treatment. 4

Children with spasmus nutans require ongoing ophthalmologic follow-up until past the amblyogenic age range, even after apparent resolution of nystagmus. 4