Page 1385 - Cote clinical veterinary advisor dogs and cats 4th

Nystagmus 699

cats. Pathologic nystagmus is a congenital Convergence–retraction nystagmus is an DIAGNOSIS
abnormality in Siamese, Tonkinese, and irregular jerk nystagmus with simultaneous Diagnostic Overview
VetBooks.ir • Dogs: pathologic nystagmus is a congenital of both eyes (OU) Pathologic nystagmus indicates vestibular Diseases and Disorders
rhythmic convergence and eyeball retraction
Burmese breeds.
dysfunction. Diagnostic testing focused on
abnormality in Doberman pinscher, cocker
• Positional nystagmus possible after spontane-
spaniel, German shepherd, and other
diseases affecting these regions.
○ Important to evaluate different head
breeds ous nystagmus resolves central and peripheral vestibular centers and
positions
ASSOCIATED DISORDERS • Head tilt (ipsilateral) Differential Diagnosis
Vestibular disease • Ataxia Peripheral causes:
• Circling (ipsilateral) • Infection (otitis media/interna)
Clinical Presentation • Falling can occur (ipsilateral) • Idiopathic
DISEASE FORMS/SUBTYPES • Ventral strabismus (ipsilateral) • Otopharyngeal polyps
Types of nystagmus: Nystagmus from central vestibular disease (not • Neoplasia
• Physiologic nystagmus: occurs in normal all signs may be present): • Hypothyroidism (rare)
animals (vestibulo-ocular reflex) with head • Jerk nystagmus • Trauma
rotation and consists of a slow phase in the ○ Horizontal, rotary, or vertical • After middle ear surgery or ear cleaning (if
opposite direction of head movement and ○ Vertical suggests central disease tympanum not intact)
a fast phase occurring in same direction of ○ Disconjugate indicates central disease • Intoxication (e.g., aminoglycosides, cleaning
head rotation. • Convergence-retraction indicates central solutions)
• Pathologic nystagmus: spontaneous lesion, often in dorsal midbrain • Congenital/hereditary
○ Present when the head is stationary and ○ Fast phase can occur in either direction Central causes:
in a normal position relative to the vestibular lesion • Neoplasia
○ Often resolves within several days of onset ○ Direction can change with head position • Idiopathic
of vestibular signs • Positional nystagmus possible after spontane- • Vascular
• Pathologic nystagmus: positional ous nystagmus resolves • Inflammation (granulomatous meningoen-
○ Nystagmus occurs in changing or unusual ○ Important to evaluate different head cephalitis, necrotizing leukoencephalitis)
head positions (head extension, dorsal or positions • Infection (bacterial, viral, fungal, proto-
lateral recumbency). • Head tilt (ipsilateral, unless paradoxical) zoal or central extension of otitis media/
○ Possible at onset of vestibular dysfunc- • Circling (ipsilateral, unless paradoxical) interna)
tion or after spontaneous nystagmus has • Ataxia • Toxic (metronidazole, marijuana, anesthesia
resolved • Proprioceptive deficits (ipsilateral) induction/recovery)
○ Occurs with peripheral or central vestibu- • Ventral strabismus (ipsilateral) • Nutritional (thiamine deficiency)
lar lesions • Cranial nerve deficits (ipsilateral) • Trauma
○ Nystagmus that changes direction with • Obtundation • Congenital/developmental
different head positions usually suggests Pendular nystagmus: congenital abnormality
a central lesion. Etiology and Pathophysiology affecting visual pathway
• Pendular nystagmus • Physiologic nystagmus occurs in normal
○ Typically nonpathologic animals with head rotation. Jerk nystag- Initial Database
• Disconjugate nystagmus mus results in the plane of rotation. Fast • Neurologic exam (p. 1136)
○ Direction of oscillation is different phase occurs in same direction as move- ○ Attempt to induce positional nystagmus.
for each eye (e.g., horizontal for the ment, and slow phase occurs in opposite ○ Absent vestibulo-ocular reflex may indicate
left eye [OS] and vertical for the right direction of movement. The fast phase is bilateral vestibular disease.
eye [OD]). induced by visual stimuli. This vestibulo- • Otoscopic exam (p. 1144)
○ Indicates central lesion ocular reflex preserves image stability on • CBC, chemistry, T 4 , and urinalysis: usually
the retina. normal
HISTORY, CHIEF COMPLAINT ○ Afferent initiating stimuli from semicir- • Tympanic bulla radiographs (limited
• Pathologic nystagmus usually has acute onset. cular canals travel to vestibular nuclei. benefit)
○ Most commonly with vestibular disease ○ Vestibular nuclei interconnect with • Thoracic radiographs and abdominal
○ Nystagmus may be unnoticed if animal motor nuclei that control extraocular ultrasound evaluates for metastatic/systemic
moves quickly or with vestibular com- muscle movement in brainstem (cranial disease
pensation (positional nystagmus possibly nerves III, IV, and VI through the medial
induced). longitudinal fasciculus). Advanced or Confirmatory Testing
• Pendular nystagmus or congenital nystagmus ○ Head movement causes reciprocating • MRI (p. 1132): preferred, due to superior
is present from birth/adolescence and is afferent stimuli from semicircular canals in soft-tissue resolution
not associated with deteriorating vestibular the plane of movement through vestibular • CT: high resolution of inner ear, less for
function. nuclei, allowing coordinated and conjugate brain
eye movements. • Cerebrospinal fluid (CSF) (p. 1323) analysis
PHYSICAL EXAM FINDINGS • Pathologic nystagmus occurs with a unilat- if intracranial disease suspected or to further
Nystagmus from peripheral vestibular disease eral lesion (e.g., single semicircular canal). evaluate for central extension of otitis media/
(not all signs may be present): Asymmetrical neural activity is perceived as interna
• Jerk nystagmus head rotation, despite the head being at rest/ • Myringotomy (cytology and culture) indi-
○ Horizontal or rotary most common motionless, inducing nystagmus. cated for otitis media/interna
○ Fast phase: away from side of vestibular • Vestibulocochlear nerve provides input from • Infectious serology considered based on
lesion and contralateral to head tilt semicircular canals to central vestibular system MRI/CSF results and environmental risk
○ Direction unchanged with head position (vestibular nuclei and rostral cerebellum). factors
○ Vertical rare with peripheral vestibular • Damage to the peripheral or central vestibular • Brainstem auditory evoked response testing
disease system produces nystagmus. can help localize vestibular disease.

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