Hereditary neuropathies are a heterogeneous group of rare genetic conditions that produce motor and sensory deficits in the extremities. Involvement of the cranial nerves (CNs) can be apparent clinically, radiographically or both, although this hasn’t been reported frequently.
Now C. Eduardo Corrales, MD, a surgeon in the Division of Otolaryngology–Head and Neck Surgery at Brigham and Women’s Hospital, Ryan A. Bartholomew, MD, a resident physician in the division, and colleagues detected a 21% prevalence of radiologic CN abnormalities in patients with hereditary neuropathies who underwent MRI.
In Laryngoscope Investigation Otolaryngology, they caution physicians not to assume these imaging findings represent pathologies requiring intervention by an otolaryngologist.
Because hereditary neuropathy is so rare (estimated prevalence 0.04%), the Brigham partnered with Massachusetts General Hospital, Stanford Medical Center, and the University of Colorado School of Medicine, to gather enough patients for the study.
The researchers analyzed the appearance of CNs on gadolinium-enhanced MRI brain or skull base scans from 39 patients with hereditary neuropathy who were imaged between 2004 and 2018. The mean patient age was 49 years (range, 3–90 years).
Prevalence of Radiographic CN Abnormalities
Eight patients (21%) had CN abnormalities on MRI:
- Three had only thickening of CNs, one had only enhancement of CNs, and four had both thickening and enhancement in the same or different CNs
- Four patients had bilateral (symmetric) abnormalities, and four patients had different CNs abnormal on the left vs. the right
- Either unilaterally or bilaterally, patients had abnormalities in CN III (n=1), CN V (n=5), CN VII distal to the internal auditory canal (IAC) (n=5), and the CN VII/VIII complex in the IAC (n=4)
Prevalence of Clinical CN Deficits
Only four of the eight patients with CN abnormalities on MRI had clinical CN deficits, and only two of them had deficits that corresponded to at least some of the abnormally appearing CNs.
Clinical CN deficits were also present in seven of the 31 patients who had no abnormalities on MRI, for a total of 11 patients with clinical deficits (28%). Examples included facial and tongue paresis and/or paresthesia, sensorineural hearing loss, tinnitus and diplopia.
Caveats for Physicians
Many of the imaging abnormalities detected in this study mimic certain neoplastic and infectious processes. Otolaryngologists, especially anterior and lateral skull base surgeons, should be aware of the possibility of misdiagnosis.
For example, otolaryngologists often interpret IAC enhancement as vestibular schwannoma, but IAC enhancement in a patient with hereditary neuropathy may be a manifestation of the patient’s underlying disease process and is less likely to require surgery or radiation therapy.
Still, CN findings warrant prudent observation. Physicians should obtain repeat imaging for these patients on an annual basis or if their clinical status changes. The interval can be extended to be longer than yearly once the imaging findings are verified to be stable.