Optic and Auditory Involvement in Demyelinating Neuropathy
Abstract & Commentary
By Michael Rubin, MD
Professor of Clinical Neurology, Weill Cornell Medical College
Dr. Rubin reports no financial relationships relevant to this field of study.
Synopsis: Demyelinating peripheral neuropathies may have subclinical evidence of optic nerve and auditory nerve dysfunction, only discovered by electrophysiological testing.
Source: Knopp M, et al. Optic and auditory pathway dysfunction in demyelinating neuropathies. Acta Neurol Scand 2014; Feb 20. doi: 10.1111/ane.12226. [Epub ahead of print].
Are the optic and auditory pathways affected in demyelinating neuropathy? To address this question, a prospective study was undertaken at the Regional Neuromuscular Clinic, Queen Elizabeth Neurosciences Center, in Birmingham, UK, between December 2011 and June 2012. Consecutive patients were recruited, with hereditary demyelinating neuropathy, encompassing Charcot-Marie-Tooth disease type 1A (CMT1A) or hereditary neuropathy with liability to pressure palsies (HNPP), or acquired demyelinating neuropathy, encompassing chronic inflammatory demyelinating polyneuropathy (CIDP) or anti-MAG neuropathy. All underwent visual evoked potential (VEP) and brainstem auditory evoked potential (BAEP) study to assess optic and auditory nerve function in the least uncomfortable manner. Diagnosis of CMT and HNPP was based on clinical and electrophysiological grounds, and confirmed by genetic testing in all patients. CIDP patients all fulfilled the 2010 updated European Federation of Neurological Societies/Peripheral Nerve Society guidelines for CIDP diagnosis, and all responded to immunomodulatory therapy. Patients with anti-MAG neuropathy all demonstrated a monoclonal IgM paraprotein with positive anti-MAG antibodies in the setting of clinical and electrophysiological findings consistent with anti-MAG neuropathy. Statistical analysis comprised Fisher’s exact tests, and Kruskal-Wallis or Mann-Whitney U-tests, with Bonferroni correction applied as warranted. P < 0.0125 was considered significant.
During the recruitment period, eight patients with HNPP (mean age 34 years), six patients with CMT1A (mean age 45 years), 10 patients with CIDP (mean age 60 years), and seven patients with anti-MAG neuropathy (mean age 70 years) were studied. One patient each with CMT1A and CIDP also had diabetes. Among anti-MAG neuropathy patients, 6/7 had abnormal VEP results, as did about half the CIDP and HNPP patients. Only 1/6 CMT1A patients had abnormal VEPs. BAEP testing demonstrated prolonged wave I latency, or prolonged wave I-wave III latency, in 5/7 patients with anti-MAG neuropathy, 5/10 with CIDP, 4/5 with CMT1A (one was excluded due to non-recordable responses from either side), and 2/8 with HNPP. Optic nerves are spared in CMT1A, but subclinical involvement is present in CIDP and HNPP, and particularly in anti-MAG neuropathy. Auditory nerve involvement is infrequent in HNPP, but is seen in the majority of patients with CIDP, anti-MAG neuropathy, and CMT1A. Subclinical involvement of the optic and auditory pathways in patients already afflicted by peripheral neuropathy may compound their neurologic disability and warrants the attention of the treating neurologist.
Cranial nerves, other than the optic and auditory nerves, may also be affected in demyelinating neuropathies. Vocal cord palsy and diaphragm weakness causing respiratory failure have been reported, rarely, in patients with Charcot-Marie-Tooth. Multifocal motor neuropathy seldom involves cranial nerves but can present as ophthalmoplegia, and may cause tongue atrophy closely mimicking motor neuron disease. Although not strictly a cranial nerve, recurrent symptoms of greater occipital neuropathy developed in a father and son with HNPP when lying supine on a floor during yoga exercise. Although idiopathic CIDP may affect cranial nerves in up to 27% (ptosis, diplopia, dysarthria), it is rare in CIDP-MGUS IgM with anti-MAG antibodies, where only 1 of 29 patients was reported with facial weakness.