Spasmus nutans (SN) is a rare, idiopathic disorder of childhood comprising the clinical triad of nystagmus, head nodding, and torticollis. This triad classically presents in the first year of life and symptoms typically resolve by 3-6 years of age (1). Recent evidence, however, points to persistence of subclinical nystagmus as measured by eye movement recordings up to age 12 (2).
The nystagmus in SN is typically horizontal and pendular, of small amplitude and high frequency, intermittent, and marked by asymmetry with occasional unilaterality. Eye movement recordings quantify an amplitude of up to 3° and a frequency of up to 15 Hz (3). Rather than being a pathologic involuntary movement, head nodding has been shown in some cases to be compensatory, with the ability to suppress nystagmus and aid vision (4,5). Similarly, the torticollis has been observed clinically and by electrooculography (EOG) recordings to dampen nystagmus by a hypothesized vestibular mechanism (6). Like the nystagmus, the head nodding and torticollis may be intermittent as well.
First described by Raudnitz (7) in 1897, SN has traditionally been considered a benign, self-limited disorder. Early observations related SN to low socioeconomic status (7-10) inadequate light exposure (7,8), rickets (7,9,10), syphilis (8), malnutrition (8), crowded living conditions (8), trauma (8), epilepsy (8), and black race. (7,9,10). Based on data derived from patient questionnaires, Wizow et al (11) reported a higher incidence of SN than of idiopathic infantile nystagmus in African Americans, Hispanics, children with decreased home luminance at birth, families of lower socioeconomic status, and patients with parental psychiatric disease. Maternal alcohol abuse (12) and child abuse/neglect (13) have also been implicated as risk factors for SN.
Intracranial pathology has been reported in association with a constellation of symptoms similar to SN since Kelly (14) first reported a case of optic glioma presenting with SN-like symptoms. There have been subsequent reports of gliomas involving the optic nerve and chiasm (15-18). Other neurologic associations include a thalamic neoplasm (19), arachnoid cyst (20), opsoclonus-myoclonus (21), diencephalic syndrome (22), and subacute necrotizing encephalomyelopathy (Leigh disease) (23).
Retinal diseases have also been associated with SN, including achromatopsia (24,25), congenital stationary night blindness (26,27), and Bardet-Biedel syndrome (28). Strabismus, refractive error, and amblyopia (29) have also been reported in SN with a noted reduction in visual acuity, higher range of refractive error, and greater need for spectacle correction compared with control populations. Strabismus and amblyopia have occurred more commonly in the eye with the greater amplitude of nystagmus (29).
With the accumulation of these reports, uncertainty regarding the prevalence of associated conditions with SN has emerged. The need for neuroimaging and electroretinography (ERG) has been widely debated, especially because clinical presentation and eye and head movement recordings are not satisfactory for predicting whether underlying conditions may be present (3). Arnoldi and Tychsen (30) have published the largest series of consecutive patients with SN and their associated conditions. Their data indicate a 1.4% prevalence of intracranial tumors and no retinal disease. Our observation has been that patients with nystagmus typical of SN often have a variety of ophthalmologic, neurologic, and systemic abnormalities. We undertook this study to determine the frequency of neurologic and retinal pathologic conditions as well as other ocular and systemic associations in patients with SN-like nystagmus.
We performed a chart review of consecutive patients examined at the Dean McGee Eye Institute and Children's Hospital of Oklahoma from January 1, 2000, to December 31, 2005, in whom nystagmus typical of SN (“SN-like nystagmus”) was diagnosed. Prior approval for this review had been granted from the Institutional Review Board of the University of Oklahoma Health Sciences Center. Inclusion was based on the clinical evaluation of eye and head movements. No quantitative eye or head movement recordings were made. We collected data on gender, age at onset of nystagmus, age at final visit at our institutions, visual acuity, laterality of nystagmus, presence of head nodding and anomalous head position, refractive error, presence of strabismus and other pertinent clinical findings, neuroimaging, and ERG.
We identified 22 patients with SN-like nystagmus (Table 1). Twelve (55%) were male and 10 were female (45%). Eight (36%) patients had monocular nystagmus and 14 patients (64%) had binocular disconjugate nystagmus. The nystagmus was horizontal in 20 patients and vertical in 2. Head nodding was present in 11 (50%) patients and torticollis in 6 (27%). Median age of onset of symptoms was 5 months (excluding 4 patients with indefinite onset by history). Patients were followed for a mean of 39.2 months with a range from 14 months to 9.2 years.
Visual acuity was reduced, as defined by Snellen acuity of less than 20/40 or abnormal Teller acuity at 38 cm, in 33 (75%) of 44 eyes at presentation and in 21 (58%) of 36 eyes at the last visit. Amblyopia was the primary cause of the decreased visual acuity in 2 eyes (6%) and was present in 4 children at the initial visit. Significant refractive errors were found in 8 eyes (36%), 7 with high myopia (>−5.00 diopters [D]) and 2 with high astigmatism (+2.50 D). None of the patients included in our study had high hyperopia (+5.00 D). An angle of strabismus greater than 20 prism-diopters was measured in 7 patients (32%); 5 of these children were esotropic and 2 were exotropic.
Other significant findings on complete ophthalmologic examination included optic disc pallor in 6 patients (27%); the pallor was bilateral in 5. Optic nerve hypoplasia was bilateral in 2 patients (9%) and was unilateral in 1 (4%). No patients had a relative afferent pupillary defect or paradoxic pupils.
Twenty patients underwent neuroimaging (91%) with evidence of chiasmal gliomas in 2 (9%) and Chiari I malformations in 2 patients (9%) and imaging evidence of “small optic nerves” in 1 patient. Other radiologic findings included an enlarged cisterna magna in 1 patient and an incidental finding of a small subdural hematoma in 1 patient.
ERG was performed in 5 patients with unexplained decreased visual acuity; 4 patients (18%) demonstrated findings consistent with cone or rod/cone dystrophy.
Seven (32%) of the 22 children had evidence of nonocular systemic abnormalities. Prematurity was evident in 5 patients (23%). Developmental delay was documented in one child. Two children (9%) had Down syndrome. One patient had neurofibromatosis type 1.
Only 3 patients (14%) had no associated ocular, intracranial, or systemic conditions.
Our study of patients with nystagmus characteristic of SN has shown that these patients frequently have underlying ocular, intracranial, or systemic abnormalities (31).
Particularly notable in our series was the presence of chiasmal gliomas in 2 patients (9%). Neither Arnoldi and Tychsen (30) nor King et al (32) reported any intracranial tumors in their series of 67 and 14 subjects, respectively. Arnoldi and Tychsen (30) reported optic nerve (ON) hypoplasia in 2 children (7%) and white matter cerebral changes on MRI in another 2 (7%). King et al (32) reported 1 patient (7%) with an empty sella and an arachnoid cyst.
Our series also included possibly contributory abnormalities in 5 other patients (23%), including ON hypoplasia, Chiari I malformation, subdural hematoma, and enlarged cisterna magna, bringing the rate of abnormal neuroimaging results to nearly one third of our patients. Of the 6 patients with abnormal MRI, 5 had evidence on clinical examination (ON hypoplasia or pallor) that suggested intracranial pathologic conditions and prompted neuroimaging. Both patients with chiasmal gliomas had ON pallor bilaterally.
The reason for the difference between our data and those of the two previous reports (30,32) is unclear. Both prior studies were performed at large tertiary care centers. However, the series of Arnoldi and Tychsen (30) was drawn primarily from a clinical practice of pediatric ophthalmology, whereas our patients were drawn from a clinical practice of pediatric ophthalmology and neuro-ophthalmology. If we had required the presence of typical nystagmus, torticollis, and head nodding for the definition of SN, perhaps fewer associated findings would have been discovered. Only 14% of our patients presented with the full clinical triad compared with 43% in the series of Arnoldi and Tychsen (30). Our study had a higher rate of neuroimaging (91%) than that of Arnoldi and Tychsen (30) (43%). Whereas King et al (32) conducted neuroimaging on all 14 of their patients, the patients underwent CT rather than MRI, so that mild enlargement of the optic nerves or chiasm could have been missed.
Four of our patients received a diagnosis of photoreceptor dystrophy. Retinal disease associated with SN has been identified previously (24-28). In a series of 8 patients with SN, Smith et al (24) reported an abnormal ERG in 3: 2 with rod dystrophy and 1 with cone-rod dystrophy. Only 5 of our patients (23%) underwent ERG, but 4 were found to have retinal dysfunction. In each of these 5 patients, persistently reduced visual acuity prompted further testing.
Patients with SN have been reported to have substantial visual acuity loss in up to 30% of eyes (1,29). These studies, however, have included only patients with negative neuroimaging. Our cohort, which included patients with abnormal neuroimaging, showed reduced visual acuity in 58% of eyes.
Our results are comparable to those of others (29,30,33,34,35) in demonstrating a high prevalence of strabismus and amblyopia. An angle of strabismus greater than 20 prism diopters was seen in 32% of our patients compared with 56% in the series of Young et al (29) and 55% for Arnoldi and Tychsen (30). Amblyopia, present in 18% of our patients, was also prevalent at rates higher than those in the general population (34,35), although not as high as the 44% seen by Young et al (29).
Our data suggest that many patients presenting with SN-like nystagmus have ocular, intracranial, and systemic associations that are not clinically obvious. In light of our findings, further investigation, including neuroimaging and ERG, should be carefully considered in these patients, particularly when visual function remains below normal for age. To avoid confusion, we propose that the term “spasmus nutans” be restricted to patients who exhibit the complete clinical triad of nystagmus, torticollis, and head nodding without optic nerve, retinal, or intracranial abnormalities and who have undergone spontaneous remission in the first decade of life.
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