Clinical Signs of Caloric Vertigo
Caloric vertigo produces characteristic nystagmus with a latency period of 5-20 seconds after irrigation, followed by vertigo and nystagmus that increase then resolve within 60 seconds, accompanied by a subjective sensation of spinning or rotational movement. 1
Key Clinical Findings During Caloric Testing
Objective Signs (Observable by Examiner)
Nystagmus characteristics:
- Latency period: 5-20 seconds (occasionally up to 1 minute) between completion of irrigation and onset of nystagmus 1, 2
- Duration: Nystagmus increases then resolves within 60 seconds from onset 1, 2
- Direction: Predictable based on temperature and ear stimulated
- Eye movements: Absence of eye movement indicates vestibular dysfunction 1
Pupillary response:
- Pupils should remain reactive; midposition or dilated fixed pupils suggest brainstem pathology 1
Subjective Symptoms (Patient-Reported)
Vertigo perception:
- False sensation of self-motion or sensation that visual surroundings are spinning/flowing 3
- Rotational or spinning quality (not vague "dizziness" or lightheadedness) 3
- Intensity correlates with the magnitude of caloric response 4
Associated symptoms:
Important Clinical Nuances
Normal vs. Abnormal Responses
Normal caloric response indicates:
- Intact peripheral vestibular function when maximum slow-phase velocity ≥15°/second 6, 7
- Symmetrical responses between ears (canal paresis <25%) 8
- Directional preponderance <40% 8
Abnormal patterns suggesting pathology:
- Unilateral weakness: Indicates peripheral vestibular lesion on affected side 9
- Directional preponderance ≥40%: May indicate Ménière's disease (14% of cases), BPPV (39% of cases), or transient benign disorder 8
- Premature reversal or perverted nystagmus: Suggests central (brainstem) pathology 9
Critical Pitfall: Absent Vertigo Perception
25% of patients report no motion sensation despite robust caloric response (maxSPV ≥15°/second) 6, 7. This phenomenon:
- Increases with age (mean age 66.5 years vs. 56.5 years in those perceiving motion) 7
- May reflect central vestibular processing deficits 6
- Associates with greater postural instability and visuospatial memory deficits 6
- Does not indicate test failure or absence of vestibular response
Age-Related Considerations
Elderly patients may:
- Report vague dizziness rather than frank spinning vertigo 3
- Have reduced perception of caloric-induced vertigo 7
- Still have intact peripheral vestibular responses on objective testing
Pediatric patients (ages 5-17):
- Show low abnormal caloric test rates (17-36% across vertigo diagnoses) 10
- Require diagnosis primarily based on clinical history rather than vestibular testing 10
Distinguishing Caloric Vertigo from Other Conditions
Caloric testing helps differentiate:
- Peripheral vestibular disorders: Unilateral weakness pattern
- Central disorders: Perverted nystagmus, absent response, or neurologic signs 9
- BPPV: Positional triggers, seconds-duration episodes (not provoked by caloric testing alone) 3, 5
- Ménière's disease: May show directional preponderance, progressive unilateral weakness with warm response reduction 8, 11
Physiologic Mechanism
The caloric second phase (reversal nystagmus) occurs when repositioning the head from vertical to horizontal after irrigation, with maximum slow-phase velocity averaging 5.0°/second (compared to 26.9°/second for first phase) 4. This reflects central vestibular asymmetry in patients with normal peripheral function 4.