Beecher, Grayson

ABSTRACT Introduction/Aims Phrenic nerve conduction studies (NCS) are regularly used in the evaluation of neuromuscular respiratory dysfunction; however, the impact of body mass index (BMI) on phrenic compound muscle action potential (CMAP) amplitudes remains poorly characterized. We evaluated the relationship between BMI and phrenic CMAP amplitudes in patients without evidence of neuromuscular diaphragmatic dysfunction. Methods We performed a retrospective secondary analysis of patients derived from two previously published cohorts from Mayo Clinic (Rochester, Minnesota) and the University of Alberta (Edmonton, Alberta) evaluating diaphragm ultrasound in suspected neuromuscular respiratory insufficiency. Patients without evidence of neuromuscular disease affecting the diaphragm who underwent bilateral phrenic NCS and diaphragm ultrasound were included. Results Seventy‐nine patients met inclusion criteria, including 36 with BMI ≥ 30 kg/m 2 . Median phrenic CMAP amplitudes were significantly lower in patients with BMI ≥ 30 kg/m 2 compared to BMI < 30 kg/m 2 (0.25 mV [ IQR 0.10–0.38] vs. 0.50 mV [0.30–0.65], p < 0.001). Low phrenic CMAP amplitudes (< 0.3 mV ) were more common in patients with obesity (58% vs. 21%, p < 0.001). BMI demonstrated a moderate negative correlation with phrenic CMAP amplitude ( ρ = −0.50, p < 0.001). Diaphragm thickness at functional residual capacity did not differ significantly between BMI groups, while diaphragm thickening ratio was modestly lower in obesity. Discussion Elevated BMI is associated with lower phrenic CMAP amplitudes in patients without evidence of neuromuscular diaphragmatic dysfunction. Reduced phrenic CMAP amplitudes in obesity may reflect technical recording limitations rather than clinically meaningful diaphragmatic dysfunction. Low‐amplitude phrenic responses in patients with obesity should be interpreted cautiously and alongside adjunctive assessments such as diaphragm ultrasound.

ABSTRACTBackgroundIdiopathic inflammatory myopathies, beyond inclusion body myositis (IBM), have demonstrated an increased risk of adverse cardiovascular outcomes, particularly myocardial infarction (MI). This study evaluated the risk of cardiovascular disease in IBM.MethodsWe conducted a non‐concurrent cohort study utilizing the expanded Rochester Epidemiologic Project, including 50 patients with IBM, matched 1:6 to age‐, sex‐, and calendar year‐matched referents without IBM. Baseline cardiovascular risk factors were recorded. Differences in baseline covariates were adjusted by the inverse probability of treatment weighting method. Participants were followed from the index date forward to determine relative risks (RR) and hazard ratios (HR) for the development of cardiovascular outcomes including MI, ischemic stroke, cardiomyopathy, congestive heart failure (CHF), and peripheral vascular disease (PVD).Results50 patients with IBM and 294 matched population referents were included. Baseline cardiovascular risk factors were similar between groups. Aspirin use was more common (28% vs. 18%, p = 0.03) and statin use less common (26% vs. 38%, p = 0.04) in IBM versus referents. Patients with IBM had an increased hazard of MI compared to referents [HR: 5.79, 95% CI (2.51, 13.36)]. The risk of MI remained consistently elevated across all models, after accounting for potential confounders. For PVD, 16/50 IBM patients versus 16/287 referents were excluded due to pre‐existing PVD at index (p < 0.001). Among remaining participants, RR for PVD was 2.38 (0.82, 6.9). IBM was not associated with an increased risk of ischemic stroke, cardiomyopathy, or CHF.ConclusionsIBM is associated with increased risk of MI compared to population referents. Heightened cardiovascular monitoring and prevention strategies are needed in IBM.

Abstract Introduction/Aims Point‐of‐care ultrasound of the diaphragm is highly sensitive and specific in the detection of neuromuscular diaphragmatic dysfunction. In some patients with neuromuscular diaphragmatic dysfunction, paradoxical thinning of the diaphragm during inspiration is observed on ultrasound; however, its frequency, electrodiagnostic associations, and prognostic significance remain uncertain. Methods Medical records of patients presenting to two electrodiagnostic laboratories (Mayo Clinic, Rochester, Minnesota and University of Alberta, Edmonton, Alberta) from January 1, 2022 to December 31, 2022, for evaluation of suspected neuromuscular respiratory failure, were reviewed. Results 214 patients were referred and 19 patients excluded due to incomplete information. Of 195 patients (384 hemidiaphragms), 104 had phrenic neuropathy, 12 had myopathy, and 79 had no evidence of neuromuscular disease affecting the diaphragm. Paradoxical thinning occurred in 31 (27%) patients with neuromuscular diaphragmatic dysfunction and was unilateral in 30, the majority (83%) having normal contralateral ultrasound. Phrenic nerve conduction studies and diaphragm electromyography results did not distinguish patients with paradoxical thinning versus without. Most patients (71%) with paradoxical thinning required non‐invasive ventilation (NIV), including 16 with unilateral paradoxical thinning. Paradoxical thinning and BMI ≥30 kg/m 2 were risk factors for requiring NIV in multivariable logistic regression analysis, with odds ratios of 2.887 (95% CI:1.166, 7.151) and 2.561 (95% CI: 1.186, 5.532), respectively. Discussion Paradoxical thinning of the diaphragm occurs in patients with prominent neuromuscular diaphragmatic dysfunction, most commonly from phrenic neuropathy, and is a significant risk factor for requiring NIV. Unilateral paradoxical thinning is sufficient for needing NIV. BMI ≥30 kg/m 2 additionally increases risk of requiring NIV in patients with neuromuscular diaphragmatic dysfunction.

Abstract Mitochondrial myopathies are frequently recognized in childhood as part of a broader multisystem disorder and often overlooked in adulthood. Herein, we describe the phenotypic and genotypic spectrum and long-term outcomes of mitochondrial myopathies diagnosed in adulthood, focusing on neuromuscular features, electrodiagnostic and myopathological findings and survival. We performed a retrospective chart review of adult patients diagnosed with mitochondrial myopathy at Mayo Clinic (2005–21). We identified 94 patients. Median time from symptom onset to diagnosis was 11 years (interquartile range 4–21 years). Median age at diagnosis was 48 years (32–63 years). Primary genetic defects were identified in mitochondrial DNA in 48 patients (10 with single large deletion, 38 with point mutations) and nuclear DNA in 29. Five patients had multiple mitochondrial DNA deletions or depletion without nuclear DNA variants. Twelve patients had histopathological features of mitochondrial myopathy without molecular diagnosis. The most common phenotypes included multisystem disorder (n = 30); mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (14); limb myopathy (13); chronic progressive external ophthalmoplegia (12); and chronic progressive external ophthalmoplegia-plus (12). Isolated skeletal muscle manifestations occurred in 27%. Sixty-nine per cent had CNS and 21% had cardiac involvement. Mutations most frequently involved MT-TL1 (27) and POLG (17); however, a wide spectrum of established and novel molecular defects, with overlapping phenotypes, was identified. Electrodiagnostic studies identified myopathy (77%), fibrillation potentials (27%) and axonal peripheral neuropathy (42%, most common with nuclear DNA variants). Among 42 muscle biopsies available, median percentage counts were highest for cytochrome C oxidase negative fibres (5.1%) then ragged blue (1.4%) and ragged red fibres (0.5%). Skeletal muscle weakness was mild and slowly progressive (decline in strength summated score of 0.01/year). Median time to gait assistance was 5.5 years from diagnosis and 17 years from symptom onset. Thirty patients died, with median survival of 33.4 years from symptom onset and 10.9 years from diagnosis. Median age at death was 55 years. Cardiac involvement was associated with increased mortality [hazard ratio 2.36 (1.05, 5.29)]. There was no difference in survival based on genotype or phenotype. Despite the wide phenotypic and genotypic spectrum, mitochondrial myopathies in adults share similar features with slowly progressive limb weakness, contrasting with common multiorgan involvement and high mortality.