A novel ex vivo model for critical illness neuromyopathy using freshly resected human colon smooth muscle

Patients suffering from critical illness are at risk to develop critical illness neuromyopathy (CINM). The underlying pathophysiology is complex and controversial. A central question is whether soluble serum factors are involved in the pathogenesis of CINM. In this study, smooth muscle preparations obtained from the colon of patients undergoing elective surgery were used to investigate the effects of serum from critically ill patients. At the time of blood draw, CINM was assessed by clinical rating and electrophysiology. Muscle strips were incubated with serum of healthy controls or patients in organ baths and isometric force was measured. Fifteen samples from healthy controls and 98 from patients were studied. Ratios of responses to electric field stimulation (EFS) before and after incubation were 118% for serum from controls and 51% and 62% with serum from critically ill patients obtained at day 3 and 10 of critical illness, respectively (p = 0.003, One-Way-ANOVA). Responses to carbachol and high-K+ were equal between these groups. Ratios of post/pre-EFS responses correlated with less severe CINM. These results support the existence of pathogenic, i.e. neurotoxic factors in the serum of critically ill patients. Using human colon smooth muscle as a bioassay may facilitate their future molecular identification.

Mononeuritis multiplex: an unexpectedly frequent feature of severe COVID-19

The prolonged mechanical ventilation that is often required by patients with severe COVID-19 is expected to result in significant intensive care unit-acquired weakness (ICUAW) in many of the survivors. However, in our post-COVID-19 follow-up clinic we have found that, as well as the anticipated global weakness related to loss of muscle mass, a significant proportion of these patients also have disabling focal neurological deficits relating to multiple axonal mononeuropathies. Amongst the 69 patients with severe COVID-19 that have been discharged from the intensive care units in our hospital, we have seen 11 individuals (16%) with such a mononeuritis multiplex. In many instances, the multi-focal nature of the weakness in these patients was initially unrecognised as symptoms were wrongly assumed to relate simply to “critical illness neuromyopathy”. While mononeuropathy is well recognised as an occasional complication of intensive care, our experience suggests that such deficits are surprisingly frequent and often disabling in patients recovering from severe COVID-19.

Pathophysiological correlations in neuropathies

This chapter begins with an explanation of the pathophysiological correlations between the recorded changes and the underlying diagnosis which allow classification into demyelinating and axonal neuropathy. Demyelinating neuropathies are discussed first. The extensive and ever expanding literature in hereditary neuropathies is highlighted. The different variants of the acute inflammatory demyelinating polyneuropathy encountered in children are discussed along with the electrodiagnostic criteria for the diagnosis. Chronic inflammatory demyelinating polyneuropathy is then covered, both in its clinical presentation and electrodiagnosis. Other causes such as MNGIE and Lyme disease are highlighted. In the section on axonal neuropathy, division into hereditary and acquired is made. The diagnosis of sensorimotor hereditary neuropathies is discussed along with primarily sensory neuropathies including ataxia telangiectasia, Friedreich’s ataxia, and abetalipoproteinaemia, finishing with discussion of the hereditary sensory and autonomic neuropathies. The many different causes of acquired axonal neuropathy are listed and discussed including neoplasia, endocrine disturbances, metabolic conditions, infective agents, autoimmune conditions, mitochondrial disease, drugs, and vitamin deficiency, finishing with critical illness neuromyopathy.

Neuromuscular Disorders

The hospital neurologist may encounter neuromuscular disorders as known chronic conditions that are exacerbated by a hospital stay, be the principal reason for admission, or develop during a prolonged hospitalization. This chapter details the presentation, diagnosis, and management of conditions affecting the peripheral nerves and neuromuscular junction, such as myasthenia gravis, Lambert-Eaton (myasthenic) syndrome, botulism, and tick paralysis; as well as muscular weakness from various causes such as rhabdomyolysis, critical illness neuromyopathy, inflammatory myopathies, muscular dystrophies, periodic paralysis, and metabolic and endocrine myopathies. Also discussed are motoneuron degeneration, including amyotrophic lateral sclerosis and progressive muscle atrophy, and neuromuscular respiratory failure.