Caloric reflex test

Caloric Reflex Test

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Diagram illustrating the caloric reflex test.

The caloric reflex test is a diagnostic procedure used to assess the function of the vestibular system, which is part of the inner ear and plays a crucial role in maintaining balance and spatial orientation. This test is commonly used in the evaluation of patients with dizziness, vertigo, and other balance disorders.

Procedure

The caloric reflex test involves the irrigation of the external auditory canal with warm or cold water or air. This temperature change induces a thermal gradient across the semicircular canals, primarily affecting the horizontal canal, which in turn stimulates the vestibular apparatus.

• Warm irrigation: Typically, water at 44°C is used. This causes the endolymph in the horizontal semicircular canal to rise, mimicking a head turn to the irrigated side, and results in a slow-phase eye movement away from the irrigated ear and a fast-phase (nystagmus) towards the irrigated ear.

• Cold irrigation: Water at 30°C is used, causing the endolymph to fall, mimicking a head turn away from the irrigated side, resulting in a slow-phase eye movement towards the irrigated ear and a fast-phase (nystagmus) away from the irrigated ear.

The test is performed with the patient in a supine position with the head elevated at 30 degrees to bring the horizontal canal into a vertical position, optimizing the response.

Interpretation

The presence and direction of nystagmus are observed and recorded. In a normal functioning vestibular system, the caloric stimulation will produce a predictable nystagmus pattern. The absence or reduction of nystagmus can indicate a dysfunction in the vestibular system on the side being tested.

• Unilateral weakness: A reduced response on one side compared to the other suggests a unilateral vestibular weakness, which can be due to conditions such as vestibular neuritis or Ménière's disease.

• Bilateral weakness: Reduced responses on both sides may indicate bilateral vestibular loss, which can occur in conditions such as ototoxicity or bilateral vestibular schwannoma.

Clinical Significance

The caloric reflex test is a valuable tool in the differential diagnosis of vestibular disorders. It helps in distinguishing between peripheral and central causes of vertigo and balance dysfunction. It is often used in conjunction with other vestibular tests such as the head impulse test and vestibular evoked myogenic potentials (VEMPs).

Related Pages

• Vestibular system
• Nystagmus
• Vertigo
• Ménière's disease
• Vestibular neuritis