P 38 Vestibular Schwannoma associated with hypertrophic neuropathy – An unusual manifestation of NF2 or not?

Abstract

We report a case of generalized hypertrophic neuropathy, which was first noted with pressure palsy after surgery of a vestibular nerve schwannoma. A 46-year-old caucasian female presented with incomplete left radial nerve palsy and incomplete left ulnar nerve palsy with loss of muscle mass between the thumb and forefinger and additional slight hypaesthesia oft he fingertips dig. 1–2. Two weeks ago she underwent surgery for a left vestibular nerve schwannoma (see picture 1). One year before neurosurgery carpal tunnel syndrome was diagnosed bilaterally. In the first interview no family history of nerve diseases was reported. Neurography of median, ulnar, tibial and peroneal nerves showed very slow nerve conduction velocities (NCV) less than 30 m/s and diminished compound motor action potentials (CMAP) with prolonged duration. Electromyography showed no signs of acute denervation. High resolution nerve sonography (HRUS) showed markedly enlarged fascicles resulting in up to 6-fold nerve cross sectional areas (see picture 2, ulnar nerve oft he right upper arm) without vascularisation. This was present in all examined nerves in different expression. Family history was complemented by the patient: Her father suffered on a “disease of muscles” (has died at the age of 45 years) and her sister, too. No signs of neurofibromatosis (1 or 2) were reported. Genetic testing on mutations typically in neurofibromatosis 1 and 2 and schwannomatosis (“NF 3”) was negative. Because of demyelinating neuropathy (suspicious Charcot-Marie-Tooth disease) duplication of PMP22 gene was examined, but it was negative. At last heterozygous MPZ-Mutation was detected. This accounts for CMT1B neuropathy. The diagnosis of CMT1B is in accordance to the neurographic and sonographic findings of peripheral nerves. The focal enlargement of some fascicles is observed in schwannomas or neurofibromas, but usually they shows vascularisation, which was not present in this case. To date an association of CMT with vestibular schwannoma is not reported in the literature. Kwon et al. (2009) described a family with CMT1A caused by duplication of the PMP22 gene. Two family members had schwannomas of the spinal cord and median nerve. The authors argue that the co-occurrence of CMT1A and schwannomas in this family would be the result of independent events, but one could not completely ignore the possibility that the coincidence of two diseases might be due to a shared genetic background. Despite the missing association of CMT with vestibular schwannoma in the literature hearing loss seems not to be rare in CMT. Sanmaneechai et al. (2015) referred to patients with CMT disease caused by MPZ gene mutations. 21 of 103 patients had hearing loss, but tests like MRI or BAER (brainstem auditory evoked response) are not given in the paper. Grider et al. (2015) found in 25 CMT patients that BAER waveforms were robust even in the absence of acoustic reflexes, except for two patients with CMT1B who had abnormal BAER recordings that were not consistent with hearing thresholds. These observations supports for the neural nature of the hearing loss in CMT1B and should improve further investigations with MRI in those patients.