- Electromyogram (EMG) shows chronic partial denervation.
- Nerve conduction studies (NCS) show a sensory>motor axonal neuronopathy in RTD Type 2 but may not show sensory involvement in RTD Type 3.
- Motor nerve conduction velocities are usually normal.
- Sensory nerve action potentials (SNAP) are often absent in RTD Type 2 with variable findings in RTD Type 3.
- Visual evoked potentials (VEP) are frequently abnormal in RTD Type 2 with variable findings in RTD Type 3.
Audiologic Test Findings
The diagnosis of ANSD in RTD is based on a characteristic pattern of results on hearing assessments performed by audiologists. In RTD the most common audiological test findings included:
- Absent or abnormal auditory brainstem response (ABR / BAEP) with cochlear microphonic present.
- Otoacoustic emissions (OAE) are often present but found to disappear over time in many patients.
- Acoustic reflexes often absent.
- Magnetic resonance imaging (MRI) is generally normal without any evidence of VIII cranial nerve hypoplasia.