Monitoring Cochlear Health With Intracochlear Electrocochleography During Cochlear Implantation: Findings From an International Clinical Investigation

OBJECTIVES

Electrocochleography (ECochG) is emerging as a tool for monitoring cochlear function during cochlear implant (CI) surgery. ECochG may be recorded directly from electrodes on the implant array intraoperatively. For low-frequency stimulation, its amplitude tends to rise or may plateau as the electrode is inserted. The aim of this study was to explore whether compromise of the ECochG signal, defined as a fall in its amplitude of 30% or more during insertion, whether transient or permanent, is associated with poorer postoperative acoustic hearing, and to examine how preoperative hearing levels may influence the ability to record ECochG. The specific hypotheses tested were threefold: (a) deterioration in the pure-tone average of low-frequency hearing at the first postoperative follow-up interval (follow-up visit 1 [FUV1], 4 to 6 weeks) will be associated with compromise of the cochlear microphonic (CM) amplitude during electrode insertion (primary hypothesis); (b) an association is observed at the second postoperative follow-up interval (FUV2, 3 months) (secondary hypothesis 1); and (c) the CM response will be recorded earlier during electrode array insertion when the preoperative high-frequency hearing is better (secondary hypothesis 2).

DESIGN

International, multi-site prospective, observational, between groups design, targeting 41 adult participants in each of two groups, (compromised CM versus preserved CM). Adult CI candidates who were scheduled to receive a Cochlear Nucleus CI with a Slim Straight or a Slim Modiolar electrode array and had a preoperative audiometric low-frequency average thresholds of ≤80 dB HL at 500, 750, and 1000 Hz in the ear to be implanted, were recruited from eight international implant sites. Pure tone audiometry was measured preoperatively and at postoperative visits (FUV1 and follow-up visit 2 [FUV2]). ECochG was measured during and immediately after the implantation of the array.

RESULTS

From a total of 78 enrolled individuals (80 ears), 77 participants (79 ears) underwent surgery. Due to protocol deviations, 18 ears (23%) were excluded. Of the 61 ears with ECochG responses, amplitudes were < 1 µV throughout implantation for 18 ears (23%) and deemed "unclear" for classification. EcochG responses >1 µV in 43 ears (55%) were stable throughout implantation for 8 ears and compromised in 35 ears. For the primary endpoint at FUV1, 7/41 ears (17%) with preserved CM had a median hearing loss of 12.6 dB versus 34/41 ears (83%) with compromised CM and a median hearing loss of 26.9 dB ( p < 0.014). In assessing the practicalities of measuring intraoperative ECochG, the presence of a measurable CM (>1 µV) during implantation was dependent on preoperative, low-frequency thresholds, particularly at the stimulus frequency (0.5 kHz). High-frequency, preoperative thresholds were also associated with a measurable CM > 1 µV during surgery.

CONCLUSIONS

Our data shows that CM drops occurring during electrode insertion were correlated with significantly poorer hearing preservation postoperatively compared to CMs that remained stable throughout the electrode insertion. The practicality of measuring ECochG in a large cohort is discussed, regarding the suggested optimal preoperative low-frequency hearing levels ( < 80 dB HL) considered necessary to obtain a CM signal >1 µV.

FRI0479 REWIRED CELL ENERGY METABOLISM IN A NOVEL KRAS-MUTATED HISTIOCYTOSIS CHARACTERIZED BY SEVERE SYNOVITIS

Background:

Histiocytoses are disorders characterized by tissue infiltration by macrophages, dendritic cells, or monocyte-derived cells. These diseases are classified in five groups based on histologic, clinical, and molecular features: Langerhans-related, cutaneous/mucocutaneous and malignant histiocytoses, Rosai-Dorfman disease, and hemophagocytic lymphohistiocytosis (1). Langerhans-related histiocytoses comprise Langerhans cell histiocytosis and Erdheim-Chester disease, both inflammatory myeloid-driven diseases characterized by clonal activating mutations along the MAPK or related pathways, most commonlyBRAFV600E, and by severe tissue and systemic inflammation (2). Here, we describe and characterize a novel, related histiocytosis chiefly manifested with severe synovial involvement.

Objectives:

Here, we describe a novel histiocytosis whose histologic and clinical picture (severe synovial involvement, systemic inflammation, skin lesions, and diabetes insipidus) differed from known histiocytic disorder. In addition, we performed molecular studies aimed at identifying causative activating mutations. Finally, by means of a dynamic 3D tissue culture system we characterized immune-metabolic mechanisms underlying disease pathogenesis and clinical response to treatment.

Methods:

The mutational status of oncogenes was determined with a mass spectrometry multiplexed genotyping approach (PentaPanel). Biospy samples were cultured in RCCSTM bioreactor (Synthecon) in the presence/absence of a MEK inhibitor (GSK1120212, 1nM), and then either processed for immunohistochemical analyses, or lysed for western blot analysis. Culture supernatants were collected for cytokine, chemokine and metabolome determination. The Bio-Plex Multiple-Cytokine Assay (Bio-Rad) and the Ella assay (ProteinSimple) were used to determine cytokine concentrations in supernatants and serum, respectively. Metabolomic studies were performed as described (3).

Results:

We identified a causative mutation in the proto-oncogeneKRAS(KRASG12D, not previously reported in related histiocytoses). In addition, 3D culture studies of patient’s biopsies revealed KRAS-driven signaling, phenotypic, and immunometabolic features. These included constitutive ERK and AKT phosphorylation, up-regulated glucose metabolism with glycolysis and TCA cycle activation, and deregulated release of pro-inflammatory cytokines IL-1β, IL-6 and TNFα. All these features reverted upon pharmacologic inhibition of the MAPK pathway. Characterization of this novel condition instructed effective treatment of the patient with the MEK inhibitor cobimetinib.

Conclusion:

Genetic, clinical, and histopathology features differentiate this condition from known histiocytic disorders. Mechanistically,KRASG12Dcauses constitutive activation of the MAPK pathway in macrophages, which results in maladaptive changes in cell energy metabolism sustaining rampant production of pro-inflammatory cytokines. Besides instructing effective treatment of this patient, these studies revealed metabolic rewiring as key to pathologic inflammatory activation of macrophages in human disease.

References:

[1]Emile JF, et al. Revised classification of histiocytoses. Blood. 2016

[2]Cavalli G, et al. The multifaceted clinical presentations and manifestations of Erdheim-Chester disease. Ann Rheum Dis. 2013

[3]Cavalli G, et al. Interleukin 37 reverses the metabolic cost of inflammation, increases oxidative respiration, and improves exercise tolerance. Proc Natl Acad Sci U S A. 2017

Disclosure of Interests:

Giulio Cavalli Consultant of: SOBI, Pfizer, Sanofi, Novartis, Paid instructor for: SOBI, Novartis, Speakers bureau: SOBI, Novartis, Giacomo De Luca Speakers bureau: SOBI, Novartis, Celgene, Pfizer, MSD, Riccardo Biavasco Employee of: Bluebird, Travis Nemkov: None declared, Angelo D’Alessandro: None declared, Rob Arts: None declared, Antonello Villa: None declared, Daniela Belloni: None declared, Greta Grassini: None declared, Giulia Cangi: None declared, Claudio Doglioni: None declared, Elisabetta Ferrero: None declared, Marina Ferrarini: None declared, Lorenzo Dagna: None declared

Cervical myelopathy secondary to ossification of the posterior longitudinal ligament in a Caucasian patient

Cervical myelopathy consequent on ossification of posterior longitudinal ligament (OPLL) is very rare in Caucasians. A 65-year-old Anglo-Saxon woman developed progressive gait disturbance, paresthesia in both legs and urinary urge incontinence. Radiological examination showed OPLL from fifth to seventh cervical vertebral level; the dense OPLL was graphically displayed by three-dimensional computerized tomography. Medial corpectomy, C5 to C7, and removal of OPLL, with subsequent fusion C4 to T1 using a free fibula graft resulted in clinical improvement. Three dimensional computerized tomographic imaging is a valuable diagnostic procedure in OPLL.