Nitrous oxide-induced myeloneuropathy.

BACKGROUND AND PURPOSE: Nitrous oxide misuse is a recognized issue worldwide. Prolonged misuse inactivates vitamin B12, causing a myeloneuropathy. METHODS: Twenty patients presenting between 2016 and 2020 to tertiary hospitals in Sydney with myeloneuropathy due to nitrous oxide misuse were reviewed. RESULTS: The average age was 24 years, and mean canister consumption was 148 per day for 9 months. At presentation, paresthesias and gait unsteadiness were common, and seven patients were bedbound. Mean serum B12 was normal (258 pmol/L, normal range [NR] = 140-750) as was active B12 (87 pmol/L, normal > 35). In contrast, mean serum homocysteine was high (51 µmol/L, NR = 5-15). Spinal magnetic resonance imaging (MRI) showed characteristic dorsal column T2 hyperintensities in all 20 patients. Nerve conduction studies showed a predominantly axonal sensorimotor neuropathy (n = 5). Patients were treated with intramuscular vitamin B12, with variable functional recovery. Three of the seven patients who were bedbound at presentation were able to walk again with an aid at discharge. Of eight patients with follow-up data, most had persistent paresthesias and/or sensory ataxia. Mobility scores at admission and discharge were not significantly correlated with the serum total and active B12 levels or cumulative nitrous oxide use. There were no significant trends between serum active B12 level and cumulative nitrous oxide use (Spearman rho = -0.331, p = 0.195). CONCLUSIONS: Nitrous oxide misuse can cause a severe but potentially reversible subacute myeloneuropathy. Serum and active B12 can be normal, while elevated homocysteine and dorsal column high T2 signal on MRI strongly suggest the diagnosis. Neurological deficits can improve with abstinence and B12 supplementation, even in the most severely affected patients.

A Meta-Analysis of Neuropsychological Functioning in the Logopenic Variant of Primary Progressive Aphasia: Comparison with the Semantic and Non-Fluent Variants.

OBJECTIVES: The logopenic variant of primary progressive aphasia (lvPPA) has disparate pathological and anatomical features when compared to the semantic (svPPA) and non-fluent (nfvPPA) variants of PPA. As such, there is increasing need for measures that improve diagnostic accuracy particularly when etiology-specific treatments become available. In the current study, we used meta-analytic methods to establish the neuropsychological profile of lvPPA and compare it to recent findings in svPPA and nfvPPA. METHODS: We extracted neuropsychological data from 51 publications representing 663 lvPPA patients and 1379 controls. We calculated Hedges' g effect sizes for nine domains of neuropsychological functioning in lvPPA and assessed the influence of demographic, disease, and task characteristics on effect size magnitude. Results obtained in lvPPA were compared to findings in svPPA and nfvPPA. RESULTS: In lvPPA, the magnitude of deficits in attention, math, visuospatial memory, and executive functioning were as prominent as language deficits. Within the language domain, lvPPA patients demonstrated greater naming than repetition deficits. Compared to svPPA and nfvPPA, lvPPA patients demonstrated greater neuropsychological deficits overall and greater impairment on attention, math, and visual set-shifting tests. CONCLUSIONS: Tests of attention, delayed visuospatial memory, visual set-shifting, and math distinguish lvPPA from svPPA and nfvPPA likely reflecting the posterior temporoparietal atrophy observed early in the course of lvPPA. These findings support the inclusion of these measures in the clinical neuropsychological assessment of lvPPA and underscore the need for additional clinicopathological and longitudinal studies of arithmetic and visuospatial memory across the PPA variants.

Successful Management of Acute Streptococcal Meningoencephalitis Complicated by Bilateral Third-Nerve Palsies, Wall-Eyed Bilateral Internuclear Ophthalmoplegia, Blindness, and Deafness: Case Report.

Introduction: Streptococcal meningoencephalitis (SME) is a rare, and frequently lethal, acute infection, and inflammation of the central nervous system parenchyma, with associated meningeal involvement. Bacterial meningoencephalitis is generally associated with high rates of morbidity and mortality, despite available antimicrobial and corticosteroid treatments. While Streptococcus pneumoniae is well recognised to cause bacterial meningitis, direct extension into the central nervous system parenchyma is rare. Case Presentation: A previously well 49-year-old man presented with sudden onset severe headache, fevers, neck stiffness, and reduced consciousness. The manifestations of SME in this patient were bilateral pupil-involving third-nerve palsies, wall-eyed bilateral internuclear ophthalmoplegia (WEBINO), bilateral blindness, bilateral deafness, a right lower motor neuron facial palsy, and upper motor neuron signs in his limbs. Initially, a partial response to high dose intravenous antibiotics occurred, but with administration of intravenous corticosteroids, further substantial resolution of the patient's neurological and neuro-ophthalmological deficits occurred. Conclusion: This case highlights the benefit of multidisciplinary diagnostic and therapeutic interventions in a case of SME complicated by bilateral pupil-involving third-nerve palsies, WEBINO, bilateral blindness, bilateral deafness, a right lower motor neuron facial palsy, and upper motor neuron signs. It appears to be the first reported case of SME with this rare collection of neuro-ophthalmological abnormalities.

Human Immunodeficiency Virus and the Nervous System.

In the era of combination antiretroviral therapy, the diagnosis and management of HIV-associated neurocognitive disorders (HANDs) has arisen. Traditionally, severe HAND was seen in those with untreated HIV infection and had a guarded prognosis. Antiretroviral therapy has provided longevity and viral control to many living with the disease, revealing an increase in prevalence of less severe forms of HAND. Despite peripheral blood and cerebrospinal fluid viral suppression, cognitive impairment occurs and progresses for reasons that are unclear at present. This article provides a review of current theories behind the development of HAND, clinical and pathologic findings, recent developments, and future research opportunities.

Potentially inappropriate medications (PIMs) in older hospital in-patients: Prevalence, contribution to hospital admission and documentation of rationale for continuation.

AIM: To establish prevalence, sequelae and documentation of potentially inappropriate medication (PIM) use in older hospital in-patients. METHODS: Notes of all patients ≥65 years old, admitted to our tertiary teaching hospital (January 2013), were retrospectively reviewed, and the Screening Tool of Older Persons' potentially inappropriate Prescriptions applied. RESULTS: Amongst 534 patients, 54.8% (284) were on ≥1 PIM at admission, 26.8% on multiple; 60.8% were discharged on a PIM. Six percent of all admissions were potentially attributable to a PIM; falls associated with risk therapies were commonest (23/30), and often (65.2%) associated with serious injury. Pre-specified subgroup analysis (n = 100) identified 101 PIMs-at-discharge amongst 47 patients. In 82.2%, a clinical rationale for continued prescription was documented, with this communicated to the GP by letter in 71.1%. CONCLUSION: PIMs were common, and contributed to admission and injury. Hospitalisation provides an opportunity for medication rationalisation, and documentation of rationale for any PIM use.

Sustained maximal voluntary contraction produces independent changes in human motor axons and the muscle they innervate.

The repetitive discharges required to produce a sustained muscle contraction results in activity-dependent hyperpolarization of the motor axons and a reduction in the force-generating capacity of the muscle. We investigated the relationship between these changes in the adductor pollicis muscle and the motor axons of its ulnar nerve supply, and the reproducibility of these changes. Ten subjects performed a 1-min maximal voluntary contraction. Activity-dependent changes in axonal excitability were measured using threshold tracking with electrical stimulation at the wrist; changes in the muscle were assessed as evoked and voluntary electromyography (EMG) and isometric force. Separate components of axonal excitability and muscle properties were tested at 5 min intervals after the sustained contraction in 5 separate sessions. The current threshold required to produce the target muscle action potential increased immediately after the contraction by 14.8% (p<0.05), reflecting decreased axonal excitability secondary to hyperpolarization. This was not correlated with the decline in amplitude of muscle force or evoked EMG. A late reversal in threshold current after the initial recovery from hyperpolarization peaked at -5.9% at ∼35 min (p<0.05). This pattern was mirrored by other indices of axonal excitability revealing a previously unreported depolarization of motor axons in the late recovery period. Measures of axonal excitability were relatively stable at rest but less so after sustained activity. The coefficient of variation (CoV) for threshold current increase was higher after activity (CoV 0.54, p<0.05) whereas changes in voluntary (CoV 0.12) and evoked twitch (CoV 0.15) force were relatively stable. These results demonstrate that activity-dependent changes in motor axon excitability are unlikely to contribute to concomitant changes in the muscle after sustained activity in healthy people. The variability in axonal excitability after sustained activity suggests that care is needed when using these measures if the integrity of either the muscle or nerve may be compromised.