COVID-19 is associated with distinct myopathic features in the diaphragm of critically ill patients

Diaphragmatic morphological post-mortem findings in critically ill COVID-19 patients: an observational study

Our study investigates the post-mortem findings of the diaphragm's muscular structural changes in mechanically ventilated COVID-19 patients. Diaphragm samples of the right side from 42 COVID-19 critically ill patients were analyzed and correlated with the type and length of mechanical ventilation (MV), ventilatory parameters, prone positioning, and use of sedative drugs. The mean number of fibers was 550±626. The cross-sectional area was 4120±3280 μm2, while the muscular fraction was 0.607±0.126. The overall population was clustered into two distinct populations (clusters 1 and 2). Cluster 1 showed a lower percentage of slow myosin fiber and higher fast fiber content than cluster 2, 68% versus 82%, p<0.00001, and 29.8% versus 18.8%, p=0.00045 respectively. The median duration of MV was 180 (41-346) hours. In cluster 1, a relationship between assisted ventilation and fast myosin fiber percentage (R2=-0.355, p=0.014) was found. In cluster 2, fast fiber content increased with increasing the length of the controlled MV (R2=0.446, p=0.006). A high grade of fibrosis was reported. Cluster 1 was characterized by fibers' atrophy and cluster 2 by hypertrophy, supposing different effects of ventilation on the diaphragm but without excluding a possible direct viral effect on diaphragmatic fibers.

Diaphragmatic thickening fraction as a predictor for intubation in patients with COVID-19

The diaphragm is the primary respiratory muscle, and its dysfunction predisposes patients to respiratory failure. Diaphragm function can be assessed by ultrasound measurement - Diaphragmatic Thickening Fraction (DTF). Respiratory viral infections (including SARS-CoV-2) can cause diaphragm dysfunction. Our case series follows three patients infected with COVID-19 pneumonia. Bedside diaphragmatic ultrasound assessments measuring DTF were trended over patient's hospital course until clinical improvement (i.e., off oxygen) or worsening (i.e., intubation). Our preliminary results suggest a correlation between DTF trends and respiratory status in patients requiring 100% oxygen. Further studies are required to assess DTF and its possible correlation to respiratory failure.

The Possible Impact of COVID-19 on Respiratory Muscles Structure and Functions: A Literature Review

The impact of SARS-CoV-2 infection on respiratory muscle functions is an important area of recent enquiry. COVID-19 has effects on the respiratory muscles. The diaphragm muscle is perturbed indirectly due to the mechanical-ventilation-induced-disuse, but also by direct mechanisms linked with SARS-CoV-2 viral infection. In this sense, a deeper understanding of the possible links between COVID-19 and alterations in structure and functions of the respiratory muscles may increase the success rate of preventive and supportive strategies. Ultrasound imaging alongside respiratory muscle strength tests and pulmonary function assessment are valid approaches to the screening and monitoring of disease, for mild to severe patients. The aim of the present review is to highlight the current literature regarding the links between COVID-19 and respiratory muscle functions. We examine from the pathophysiological aspects of disease, up to approaches taken to monitor and rehabilitate diseased muscle. We hope this work will add to a greater understanding of the pathophysiology and disease management of respiratory muscle pathology subsequent to SARS-CoV-2 infection.

Myopathy as a cause of fatigue in long-term post-COVID-19 symptoms: Evidence of skeletal muscle histopathology

Background and purpose

Among post‐COVID‐19 symptoms, fatigue is reported as one of the most common, even after mild acute infection, and as the cause of fatigue, myopathy diagnosed by electromyography has been proposed in previous reports. This study aimed to explore the histopathological changes in patients with post‐COVID‐19 fatigue.

Methods

Sixteen patients (mean age = 46 years) with post‐COVID‐19 complaints of fatigue, myalgia, or weakness persisting for up to 14 months were included. In all patients, quantitative electromyography and muscle biopsies analyzed with light and electron microscopy were taken.

Results

Muscle weakness was present in 50% and myopathic electromyography in 75%, and in all patients there were histological changes. Muscle fiber atrophy was found in 38%, and 56% showed indications of fiber regeneration. Mitochondrial changes, comprising loss of cytochrome c oxidase activity, subsarcollemmal accumulation, and/or abnormal cristae, were present in 62%. Inflammation was found in 62%, seen as T lymphocytes and/or muscle fiber human leukocyte antigen ABC expression. In 75%, capillaries were affected, involving basal lamina and cells. In two patients, uncommon amounts of basal lamina were found, not only surrounding muscle fibers but also around nerves and capillaries.

Conclusions

The wide variety of histological changes in this study suggests that skeletal muscles may be a major target of SARS‐CoV‐2, causing muscular post‐COVID‐19 symptoms. The mitochondrial changes, inflammation, and capillary injury in muscle biopsies can cause fatigue in part due to reduced energy supply. Because most patients had mild–moderate acute affection, the new variants that might cause less severe acute disease could still have the ability to cause long‐term myopathy.

Neurologic complications of coronavirus and other respiratory viral infections

In humans, several respiratory viruses can have neurologic implications affecting both central and peripheral nervous system. Neurologic manifestations can be linked to viral neurotropism and/or indirect effects of the infection due to endothelitis with vascular damage and ischemia, hypercoagulation state with thrombosis and hemorrhages, systemic inflammatory response, autoimmune reactions, and other damages. Among these respiratory viruses, recent and huge attention has been given to the coronaviruses, especially the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic started in 2020. Besides the common respiratory symptoms and the lung tropism of SARS-CoV-2 (COVID-19), neurologic manifestations are not rare and often present in the severe forms of the infection. The most common acute and subacute symptoms and signs include headache, fatigue, myalgia, anosmia, ageusia, sleep disturbances, whereas clinical syndromes include mainly encephalopathy, ischemic stroke, seizures, and autoimmune peripheral neuropathies. Although the pathogenetic mechanisms of COVID-19 in the various acute neurologic manifestations are partially understood, little is known about long-term consequences of the infection. These consequences concern both the so-called long-COVID (characterized by the persistence of neurological manifestations after the resolution of the acute viral phase), and the onset of new neurological symptoms that may be linked to the previous infection.