Use of Letermovir for Primary and Secondary Cytomegalovirus Prophylaxis in Abdominal Organ Transplantation: A Single Center Experience

Background: Cytomegalovirus (CMV) infection after abdominal organ transplantation is associated with increased morbidity and mortality. The use of valganciclovir for CMV prophylaxis is limited by drug-induced myelosuppression and potential emergence of resistance. Letermovir is approved for primary CMV prophylaxis in CMV seropositive allogeneic hematopoietic cell transplant recipients. However, it is increasingly used off-label for prophylaxis in solid organ transplant (SOT) recipients. Methods: Based on pharmacy records, we examined retrospectively the use of letermovir for CMV prophylaxis in abdominal transplant recipients initiated on therapy at our center from January 1, 2018 through October 15, 2020. Data were summarized using descriptive statistics. Results: Twelve episodes of letermovir prophylaxis occurred in ten patients. Four patients received primary and 6 patients received secondary prophylaxis during the study period, with 1 patient receiving letermovir secondary prophylaxis on 3 separate occasions. All patients receiving letermovir for primary prophylaxis had successful outcomes. However, letermovir secondary prophylaxis was unsuccessful in 5 of the 8 episodes (62.5%) due to breakthrough CMV DNAemia and/or disease. Only 1 patient discontinued therapy due to adverse effects. Conclusion: Although letermovir was generally well tolerated, the high rate of failure when used as secondary prophylaxis was noteworthy. Additional controlled clinical trials assessing the safety and efficacy of letermovir prophylaxis in SOT recipients are warranted.

Unmet Needs and Strategies to Promote Patient Engagement in the Arab World: Experts' Opinion

BACKGROUND

The significance of patient engagement (PE) is widely acknowledged as a crucial element in fostering positive health outcomes, elevating care quality, and streamlining healthcare systems. Despite its recognized advantages, the level of patient engagement in Arab nations remains suboptimal.

METHODS

A high-level assembly was convened in Dubai with 11 distinguished patient advocates from diverse Arab countries. Their collective aim was to dissect the obstacles hindering patient engagement in the Arab world and propose pragmatic strategies to surmount them. First, a series of five open-ended, comprehensive questions were posed and thoroughly deliberated upon. Second, the barriers to patient engagement within the experts' respective communities were debated. A qualitative thematic analysis was conducted and two reports were generated by two independent researchers from the original meeting recordings.

RESULTS

This paper highlights the importance of patient engagement in advancing healthcare and categorizes barriers to patient engagement as patient-related, provider-related, or system/government-related. The experts identified the primary gaps in patient engagement and proposed strategies to promote it, with a primary focus on motivating both patients and providers toward shared decision-making.

CONCLUSIONS

This paper amalgamates the insights and recommendations distilled from the expert gathering, juxtaposing them within the broader context of existing literature on patient engagement. Offering a comprehensive viewpoint, this article delves into the challenges and opportunities intrinsic to bolstering patient engagement in the Arab world. Moreover, it spotlights invaluable tools often overlooked within Arab countries. The practical insights provided here can serve as a roadmap for administrators and decision-makers, providing guidance to enhance patient engagement on both a national and institutional scale.

Safety and immunogenicity of a tetravalent and bivalent SARS-CoV-2 protein booster vaccine in men

The safety and immunogenicity of a protein-based tetravalent vaccine SCTV01E that contains spike protein ectodomain (S-ECD) of Alpha, Beta, Delta and Omicron BA.1 are assessed and compared with bivalent protein vaccine SCTV01C (Alpha and Beta variants) and monovalent mRNA vaccine (NCT05323461). The primary endpoints are the geometric mean titers (GMT) of live virus neutralizing antibodies (nAb) to Delta (B.1.617.2) and Omicron BA.1 at day 28 post-injection. The secondary endpoints include the safety, day 180 GMTs against Delta and Omicron BA.1, day 28 GMTs to BA.5, and seroresponse rates of neutralizing antibodies and T cell responses at day 28 post-injection. 450 participants, comprising of 449 males and 1 female, with a median age (range) of 27 (18-62) years, are assigned to receive one booster dose of BNT162b2, 20 µg SCTV01C or 30 µg SCTV01E and completed 4-week follow-up. All SCTV01E related adverse events (AEs) are mild or moderate and no Grade ≥3 AE, serious AE or new safety concerns are identified. Day 28 GMT of live virus neutralizing antibodies and seroresponse against Omicron BA.1 and BA.5 with SCTV01E are significantly higher than those with SCTV01C and BNT162b2. These data indicate an overall neutralization superiority with tetravalent booster immunization in men.

Management of Cepacia syndrome in an immunocompetent non-cystic fibrosis adult patient

Burkholderia cepacia complex (BCC) is nonfermenting, Gram-negative bacteria known to cause high morbidity and mortality. They commonly affect patients with cystic fibrosis (CF) and are often missed in those without, despite being fatal if left untreated. We report a case of cepacia syndrome in a 42-year-old, immunocompetent man without CF who initially presented with sepsis secondary to pneumonia. Multiple isolates from blood, synovial fluid, and wound swabs grew BCC. Treatment options and management strategies remain poorly understood for BCC in general and in cases without CF in specific. We successfully treated the patient using a combination of intravenous and inhalational antibiotics. This case report elaborates on the disease presentation, investigations, and management strategy employed to treat this rare infection.

Chest computed tomography and chest X-ray in the diagnosis of community-acquired pneumonia: a retrospective observational study

Objectives

To compare the yield of early combined use of chest X-ray (CXR) and chest computed tomography (CT) in patients diagnosed with community-acquired pneumonia (CAP) presenting to the emergency department (ED) and assess the impact of chest CT on the initial diagnosis.

Methods

The medical records of 900 patients who presented to the ED and were diagnosed with CAP over a 1-year period were reviewed, and 130 patients who underwent CXR and chest CT within 48 hours were selected. CXR findings were classified as positive, negative, or inconclusive for CAP. Chest CT findings were defined as positive, negative, inconclusive, or positive with add-on to the CXR findings. CT was classified as having no benefit, large benefit, or moderate benefit based on the chest CT and CXR findings.

Results

Chest CT results were positive in 90.7% of patients, with 41.5% being newly diagnosed after negative or inconclusive CXR and 21.5% being diagnosed with add-on to the CXR findings. CT had large, moderate, and no benefit over CXR in diagnosing or excluding CAP in 45.3%, 21.5%, and 33.1% of patients, respectively.

Conclusion

Early chest CT may be used to compliment CXR in the early diagnosis of CAP among patients in the ED.

Effect of cereal type and plant extract addition on the growth performance, intestinal morphology, caecal microflora, and gut barriers gene expression of broiler chickens

Feeding broiler chickens on diets based on cereal grains of high non-starch polysaccharides content such as wheat and barley can negatively impact their performance and gut health. Plant extracts can be used as a potential tool to alleviate these negative effects. The present study assessed the effects of dietary cereal type and the inclusion of a plant extract blend (PEB) on the growth performance, intestinal histomorphology, caecal microflora, and gene expression of selected biomarkers for gut integrity in broiler chickens in a 42-d experiment. Ross-308 male broilers were assigned into different dietary treatments and fed on two cereal types (corn- vs. wheat/barley-based) with/without added graded concentrations of a PEB (0, 250, 500, 1000, and 2000 mg/kg diet). There were no significant differences in the growth performance parameters, intestinal histomorphology, and caecal microflora due to the impact of dietary cereal type. However, lactobacilli count in the caecal microflora was increased in the group fed on a corn-based diet. The PEB supplementation especially at a level of 500 to 1000 mg/kg diet significantly increased the average BW and decreased the feed conversion ratio. It also increased the villi length of duodenum, jejunum, and ileum, decreased the duodenal crypt depth, and increased the villi length to crypt depth ratio in the duodenum, jejunum and ileum. Supplementation of the PEB decreased the total bacterial and coliform count and increased the lactobacilli count in a linear pattern. Gene expression of Occludin and Junction Adhesion Molecule was significantly increased in the PEB supplemented diets, whereby no influence was observed on mucin expression. In conclusion, supplementation of a PEB at levels of 500-1000 mg/kg can be used as a tool to improve broiler performance and gut health.

Current choices of antibiotic treatment for Pseudomonas aeruginosa infections

PURPOSE OF REVIEW

Pseudomonas aeruginosa is one of the most feared nosocomial pathogens. Treatment of P. aeruginosa infections is challenging because of the limited choices of antibiotics and the emergent resistance of the pathogen. The present review aims at addressing the management of P. aeruginosa infections and highlighting the novel antibiotics that show a future promising role.

RECENT FINDINGS

Novel fluoroquinolones have been recently introduced and show favorable activity. New combinations of β-lactams/β-lactamase inhibitors have been studied in various indications of infections because of P. aeruginosa. Cefiderocol, a new cephalosporin, shows very promising results against P. aeruginosa. Currently, combination therapy is only recommended in limited scenarios. Extended-infusion of β-lactams exhibit clinical benefit. Bacteriophage therapy is a growing field of interest and may have an impactful effect on the treatment of resistant P. aeruginosa.

SUMMARY

Factors that guide clinical decisions for empiric and directed P. aeruginosa therapy include the epidemiology, the patient's risk factors, the site of infection, and the available treatment options. Conventional antipseudomonal antibiotics have been used successfully for a long time, but the increase in worldwide resistance necessitates the need for newer agents. Antimicrobial stewardship is essential to preserve the new drugs and prevent future development of resistance.

Unusual Death; Light Microscopy Solves The Mystery With An Archetypal Depiction Of An Unexpected Rare Cause

Casestudy: Hypertrophic cardiomyopathy is a heterogeneous disease with a number of phenotypes. We present the rarest phenotype, 1% of all cases, the midventricular obstructive type. It is characterized by hypertrophy in the mid portion of the left ventricle involving the papillary muscles, resulting in systolic intraluminal obstruction of the mid-ventricle. An unusual case of a 41-year-old male who died suddenly while hiking. He had no past medical history except for hyperlipidemia. He had no history of hypertension, with documented repeated normal blood pressures. No family history of cardiac problems, sudden death, or death at young age. On autopsy examination, his heart weighed 540 grams. The left ventricle was concentrically hypertrophied, 1.8 cm in thickness, with prominent papillary muscles and small lumen. The interventricular septum measured 1.8 cm in thickness, with increase sub-aortic wall thickness. Microscopic examination revealed myocyte hypertrophy with boxcar-like nuclear enlargement and interstitial fibrosis. There was myocardial fiber disarray. Intramural vessels showed dysplastic changes with medial thickening and narrowing of the lumen. Genetic cardiomyopathy panel testing on paraffin-embedded sections was negative; testing-on whole blood is preferred but body was embalmed before autopsy. The immediate cause of death was hypertrophic cardiomyopathy leading to pulmonary edema with potential complications as arrhythmias and low cardiac output. This case highlights the importance of light microscopy in the diagnostic process despite negative genetics. It also underscores the crucially of adopting better strategies to identify the disease since sudden death occurs frequently in those where diagnosis is missed during life.

Mistaken Identity: A Rare Tumor Unexpectedly Identified in a Renal Transplant Recipient’s Obsolescent Native Kidney

Casestudy: Multilocular cystic clear cell renal cell neoplasm of low malignant potential is a rare entity, comprising 1–2% of all renal tumors. This is mostly due to that the majority (90%) are incidentally found by radiologic exams performed for other reasons. Cystic lesions are not uncommon in patients over 50 years old and are difficult to assess surgically. Therefore, it is even more important to recognize this subtype of renal cell neoplasm histopathologically, as these tumors behave very differently from their other counterparts. We report a case of a 63- year-old female renal transplant recipient who subsequently presented with bilateral native nephrolithiasis and left flank pain. Imaging demonstrated the calculi, for which the patient underwent left nephrectomy to relieve her pain. On gross examination, the cut surface of the kidney revealed a well-circumscribed, well-encapsulated, multiloculated cystic lesion at the upper pole measuring 1.9 cm with thin fibrous septae. Microscopically, the lesion was composed of loculations and septations as were observed grossly. These spaces were lined by one to two layers of cells with clear cytoplasm, some of which were present within the septal walls. The nuclei were haphazardly distributed within the cytoplasm of the cells. They were grade 2 according to the International Society of Urologic Pathology grading scale. The tumor cells demonstrated CK7 positivity. To our knowledge, this is the first case of multilocular cystic clear cell renal cell neoplasm of low malignant potential in a transplant recipient’s native end stage kidney mistaken for renal calculi.

Simultaneous Brucella breast and pacemaker infection

Infection with Brucella spp. is endemic to the Middle East and the eastern Mediterranean basin. Brucellosis can mimic infectious and non-infectious febrile illnesses and therefore it can pose a diagnostic challenge. A wide range of deep-seated infections have been ascribed to brucellosis including breast abscesses and infections of prosthetic endovascular devices. The latter are usually rare but difficult to treat short of excision of the infected device. Here, we present the case of a middle-aged Lebanese woman who presented with simultaneous breast abscesses and a pacemaker infection due to brucellosis. To our knowledge, a similar manifestation has not been reported in the literature.

Correction to: Mucormycosis in hospitalized patients at a tertiary care center in Lebanon: a case series

Unfortunately, the original version of this article contains mistakes. The names "Jean El-Cheikh" and Aline El Zakhem were spelled incorrectly.

Correction to: Mucormycosis in hospitalized patients at a tertiary care center in Lebanon: a case series

The spelling of the name "Ali Bazarbachi" was incorrect.

Mucormycosis in hospitalized patients at a tertiary care center in Lebanon: a case series

PURPOSE

Mucormycosis (MCM) is a rare fungal infection affecting people with impaired immunity. Data related to MCM from Lebanon are scarce. The aim of this study is to shed light on the epidemiology, incidence, and outcome of patients with MCM hospitalized at a tertiary care center in Lebanon.

METHODS

We conducted a retrospective chart review between Jan 1, 2008 and Jan 10, 2018. All patients with proven or probable MCM were included.

RESULTS

A total of 20 patients were included. Their median age was 49 years and the majority were males. Comorbidities included mainly hematologic malignancy and diabetes mellitus. Most common sites of involvement were rhino-orbital and pulmonary, respectively. The number of MCM cases/10.000 hospital admissions increased significantly between 2008 and 2017 (0.47 vs. 1.18; P < 0.05). A liposomal amphotericin B formulation alone or in combination with other antifungals was used as a first line agent in all patients. All-cause mortality was 60%; however, death was attributed to MCM in 20% of cases.

CONCLUSION

The incidence of MCM has significantly increased over the past 10 years at our institution, most likely due to the increasing patient population at risk. Understanding the epidemiology of MCM in our setting would help guide antifungal therapy.

The effect of androgen deprivation therapy on CD4/CD8 T cells in HIV-negative patients receiving definitive 3D radiation treatment for their prostate carcinoma: Final report of a prospective study

11056

Background: CD4 and CD8 T cells play critical roles in human immunity. The aim of this prospective study is to explore the correlation of the absolute CD4/CD8 T cell counts and total testosterone in patients receiving androgen deprivation therapy (ADT) with goserelin acetate and definitive radiation treatment (RT) for their prostate cancer. Methods: Thirty-four HIV-negative patients were included in this study between June 2006 and January 2007. All patients had a baseline total testosterone level (T), PSA, CD4 and CD8 T cell counts. CD4/8 T cells count was measured using flow cytometry. All patients received 6 months of ADT prior to (baseline) and during RT to the prostate. Subsequent blood samples were taken at 2, 8, 12 and 24 months. Blood samples were taken between 8–10 am to control for diurnal variations in CD4/CD8 T cell counts and T levels. To study the correlation of T with CD4/8 T cell changes, the Spearman correlation coefficient was calculated. The study was approved by the appropriate Ethics Committee. Results: Median age for the study patients was 68 years. At baseline, median testosterone level was 350 ng/dL, median CD4 T cell count was 1055 mm3, and median CD8 T cell count was 644 mm3. None of the patients received anti-androgens. At two months, testosterone was at the castrate and subnormal levels in 85% and 100% of the patients, respectively. The lower testosterone levels resulted in significant reduction of CD4 and CD8 T cell counts at 2, 8, 12 and 24 months compared to baseline counts. This effect was more pronounced for CD4 T cells at all time points (p=<0.02). At 24 months, when total testosterone levels were increasing, CD4 and CD8 T cell counts were also following these upward trends. The seen correlation between lower testosterone and decline in CD4 and CD8 T cells was only statistically significant in older patients (>65 years) and was not associated with significant decline in total white blood cell counts. Conclusions: CD4/CD8 T cell counts are sensitive to changes in total testosterone levels. Lower testosterone levels negatively affecting CD4/CD8 T cells counts at all study time points. Since CD4/CD8 T cells play major roles in cellular immunity, further studies are warranted

No significant financial relationships to disclose.

Predicting clinical outcomes for newborns using two artificial intelligence approaches

Two different approaches, based on artificial neural networks (ANN) and fuzzy logic, were used to predict a number of outcomes of newborns: How they would be delivered, their 5 minute Apgar score, and neonatal mortality. The goal was to assess whether the methods would be comparable or whether they would perform differently for different outcomes. The results were comparable for Correct Classification Rate (CCR) and Specificity (true negative cases). Sensitivity (true positive cases) was slightly higher for the back-propagation feed-forward ANN than using the Fuzzy-Logic Classifier (FLC). Since this is one single database and a very large one, it is possible that the FLC would perform better than the ANN for very small databases, as shown by some of the co-authors in the past. The next step will be to test a small database with both methods to assess strengths and weaknesses with the intent to use both if needed with some medical data in the future.

Carboplatin ototoxicity: an animal model

A new animal model of ototoxicity is presented using intravenous carboplatin in adult chinchillas. A range of physiological and morphological effects was produced using doses calculated from the recommended therapeutic range (200-400 mg/m2). Auditory thresholds to tone pips stimuli were monitored using brain stem evoked responses (ABR). Cochlear histopathology was studied by light microscopy (LM) and ultrastructural hair cell abnormalities investigated with scanning electronmicroscopy (SEM). Carboplatin in this animal model predominantly affected the inner hair cells. This may provide an important model for the study of selective loss of the main afferent input in the auditory system.

Impact of the safe water system on water quality in cyclone-affected communities in Madagascar

Cyclone Hudah struck the northeastern coast of Madagascar in the spring of 2000. Over a 5-month period, 11 700 relief kits consisting of bottles of water disinfectant and foldable jerry cans were distributed to the affected population. Five months after the cyclone, a survey was conducted in 12 villages to determine the impact of these relief kits on water quality. Seventy-six percent of the surveyed households reported using jerry cans, and 65% reported using the disinfectant. Stored water in households using both products had significantly less microbiological contamination than stored water in other households. To improve the prospects for a sustainable intervention, the response plan for future disasters should incorporate a transition to recovery and development, including formative research into local customs, beliefs, and water handling habits, and funding support to initiate social marketing.

Gemcitabine and UFT plus oral calcium folinate: phase I study

Gemcitabine (Gemzar) is a nucleoside analog increasingly used in the treatment of a variety of solid tumors. DNA synthesis is inhibited by gemcitabine by masked chain termination and via inhibition of ribonucleotide reductase. Synergy may exist between gemcitabine and other antimetabolites, including 5-fluorouracil. The varying patterns of dose-limiting toxicities to gemcitabine and UFT (uracil and tegafur in a 4:1 molar ratio) plus oral calcium folinate (Orzel) permit their use in combination. The primary aim of this phase I study is to determine the maximum tolerated doses of gemcitabine and UFT plus oral calcium folinate in patients with a variety of solid tumors. Only eight patients have been recruited to date, with myelosuppression being the main toxicity observed.

Plasticity of tonotopic maps in auditory midbrain following partial cochlear damage in the developing chinchilla

There is substantial reorganization of the midbrain (inferior colliculus) tonotopic map following neonatally induced partial cochlear lesions in the chinchilla. The most obvious feature of this remapping is a large "iso-frequency" region in the ventral sector of the central nucleus of inferior colliculus (ICC). Neurons in this region exhibit similar threshold and tuning properties, with a common characteristic frequency which corresponds to the high-frequency audiometric cutoff. This overrepresented frequency range also corresponds to the high-frequency border of the cochlear lesion. Alterations to the tonotopic map corresponding to lower frequencies, in more dorsal regions of ICC, depend on the extent and degree of the cochlear lesion. When there is minimal damage to apical (low-frequency) cochlear areas, the dorsal ICC has relatively normal frequency representations. With more extensive apical cochlear lesions there is a corresponding disruption of ICC tonotopic representation of the low frequencies. We conclude that the tonotopic map within the ICC can become (re)organized postnatally according to the abnormal pattern of neural activity from the auditory periphery. Similar reorganization can be expected to occur in human infants with a partial cochlear hearing loss from birth.

Antimicrobial activity of Cassia alata from Malaysia

Ethanolic extract of Cassia alata leaves was investigated for its antimicrobial activities on several microorganisms including bacteria, yeast, dermatophytic fungi and non-dermatophytic fungi. In vitro, the extract exhibited high activity against various species of dermatophytic fungi but low activity against non-dermatophytic fungi. However, bacterial and yeast species showed resistance against in vitro treatment with the extract. The minimum inhibitory concentration (MIC) values of the extract revealed that Trichophyton mentagorphytes var. interdigitale, Trichophyton mentagrophytes var. mentagorophytes, Trichophyton rubrum and Microsporum gypseum had the MIC of 125 mg/ml, whereas Microsporum canis had the MIC of 62.5 mg/ml. The inhibition can be observed on the macroconidia of Microsporum gypseum which resulted in structural degeneration beyond repair. The mechanism of inhibition can be related to the cell leakage as observed by irregular, wrinkle shape and loss in rigidity of the macroconidia.

Cochlear function after selective inner hair cell degeneration induced by carboplatin

The ototoxicity of carboplatin, a second generation anti-cancer agent, was examined using the chinchilla as an animal model. In animals treated with a clinical therapeutic dose (400 mg/m2), the dominant degenerative change is to inner hair cells (IHCs). This is in sharp contrast to most other ototoxic agents, which damage primarily the outer hair cells (OHCs). Functional changes to the cochlea have been evaluated in carboplatin treated subjects by recording cochlear action potentials (CAP) and cochlear microphonics (CM); cochlear lesions were evaluated using scanning electron microscopy. In carboplatin treated animals, CAP thresholds to tone-pip stimuli were elevated in proportion to IHC damage in corresponding cochlear regions. In contrast, CM amplitudes and 'thresholds' remained close to normal in most cases, reflecting the preservation of OHCs in the basal turn. These results indicate a high degree of independence between the inner and outer hair cell systems in the cochlear transduction mechanism. We suggest that this species-specific preparation with selective IHC loss will provide a valuable tool for studying, separately, the role of OHCs in both afferent and efferent cochlear function.

Selective inner hair cell ototoxicity induced by carboplatin

Carboplatin is a second-generation platinum antineoplastic agent. It has biological activity similar to cisplatin and is currently recommended for the treatment of ovarian cancer. In clinical use, carboplatin appears less ototoxic than cisplatin. This paper reports the ototoxic effects of carboplatin, in doses equivalent to the clinical use of the drug, in the chinchilla. Intravenous carboplatin 200 to 400 mg/m2 by bolus injection caused significant ototoxicity in this model as revealed by brainstem evoked responses (ABR audiometry). The cochlear pathology as seen by scanning electron microscopy revealed predominantly inner hair cell (IHC) stereocilia damage. Furthermore, the extent (grade) of the morphological lesions appears to be well correlated with the auditory brainstem response pattern of threshold elevation.

Neonatal cochlear hearing loss results in developmental abnormalities of the central auditory pathways

We have used animal models of long term neonatal cochlear hearing loss to study developmental plasticity of the central auditory pathways. Newborn chinchilla pups and feline kittens were treated with the ototoxic drug amikacin, so as to induce basal lesions in the cochlea. At maturity these animals were used in single unit electrophysiological mapping studies, in which the cochleotopic organization of primary auditory cortex (of the cat) and the inferior colliculus of the midbrain (in the chinchilla) were mapped. We have observed, both in the midbrain and auditory cortex, massive reorganization of frequency representation. Most striking were the presence of large monotonic regions (i.e. large areas in which all neurons have similar tuning properties). Cochlear lesions which involve inner hair cells clearly modify the normal development of cochleotopic representation in the midbrain and cortical regions. We suggest that similar abnormal patterns of frequency representation will exist in human subjects with long term neonatal hearing loss.

The effects of long-term cochlear hearing loss on the functional organization of central auditory pathways

We have developed an animal model of neonatal high-frequency cochlear hearing loss to investigate the long-term effects on the central auditory pathways. Specifically, we have induced basal cochlear lesions in newborn kittens using the ototoxic aminoglycoside, amikacin. We have monitored the consequent auditory threshold elevations using auditory brainstem evoked responses (ABR) to tone pip stimuli. In the mature animal we have mapped tonotopic (cochleotopic) representation in primary auditory cortex (AI) using standard micro-electrode recording techniques, and we show that this map becomes massively re-organized. In particular, one frequency area that corresponds to the high frequency cut-off slope of the subject's audiogram appears to become greatly expanded, in some cases to take up 75% of AI surface. In general, the development of normal cochleotopic or tonotopic representation in cortex appears to depend upon the integrity of ascending sensory input from the cochlea particularly during early stages of development. With the clinician in mind, we discuss our findings in relation to practical issues.

Auditory evoked potentials in cats with neonatal high frequency hearing loss. Evidence of abnormal frequency representation in the midbrain

We have recorded auditory evoked potentials, of both neurogenic and myogenic origin, in cats having neonatal high frequency cochlear hearing loss. Using frequency specific stimuli (tone pips) and by measuring responses near to threshold, we have probed tonotopic (or cochleotopic) representation within the brainstem-midbrain auditory pathway. At stimulus frequencies corresponding to the high frequency cut-off of the cats' audiograms we have observed enhanced amplitudes of both auditory brainstem evoked responses (ABR) and postauricular myogenic (PAM) potentials. We interpret our findings as evidence of a larger than normal population of neurons tuned to this frequency region. We suggest that such abnormal frequency representation results from a long-term sensory deficit caused by lesions to the basal, high frequency region of the cochleas.