Clinical case · clinician

Pulsatile tinnitus and pressure-induced vertigo with a normal CDP

Vignette

A 47-year-old academic complains of pulsatile tinnitus, autophony (her own voice sounds unusually loud in the right ear), and brief episodes of vertigo precipitated by coughing, sneezing, or lifting heavy objects. She also describes a sense of disequilibrium when exposed to loud sounds. She has had previous extensive vestibular work-up at other centres without diagnosis. Bedside examination shows down-beating nystagmus with positive Valsalva manoeuvre and a positive Tullio phenomenon (vertical nystagmus on loud sound exposure). Audiometry shows a low-frequency air-bone gap on the right with intact bone conduction. cVEMP thresholds are abnormally low on the right.

CDP findings

SOT pattern vs normal
Normalage norm 700255075100EQS95C1EO ·F93C2EC ·F90C3EO ·F·Sw87C4EO ·Sw76C5EC ·Sw69C6EO ·Sw·Sw
MCT — medium-amplitude backward translation
platform156 ms-100-500+50+100COP mm0200400600800100012001400Normal · backward · medium
ADT — sway energy across five trials per direction
sway energy025507510067T140T235T332T428T5Toes upadapting61T148T237T330T430T5Toes downadapting

Audiometric findings

Superior canal dehiscence — low-frequency air-bone gap on the affected (right) ear with intact bone conduction.

2505001k2k4k8kFrequency (Hz)020406080100Threshold (dB HL)NormalMildModerateMod-severeSevereProfoundRight (AC)Left (AC)Bone: < right, > left

Superior canal dehiscence produces a 'third window' lesion. Air conduction is degraded at low frequencies because some of the acoustic energy is shunted through the dehiscence; bone conduction is paradoxically supranormal at low frequencies because the third window improves transmission of bone-conducted sound. The result is an air-bone gap that mimics conductive loss — but with intact middle-ear function clinically and on tympanometry. The CDP is typically normal in SCD; the audiometric and cVEMP findings carry the diagnosis.

Single-best-answer

Her CDP is essentially normal. What is the most likely diagnosis, and what is the appropriate use of CDP in this clinical context?

Teaching point. Superior semicircular canal dehiscence syndrome is a classic example of a vestibular diagnosis for which CDP is unhelpful — the test probes quiet stance, not pressure- or sound-induced symptoms. The diagnosis rests on the clinical picture (Tullio phenomenon, Valsalva-induced vertigo, autophony), audiometric findings (low-frequency air-bone gap with intact bone conduction), cVEMP findings (abnormally low thresholds on the affected side), and high-resolution CT confirmation. Surgical management (middle fossa or transmastoid canal plugging or resurfacing) is reserved for disabling symptoms.

References