Small-nerve-fiber pathology in critical illness documented by serial skin biopsies

Critical illness-associated weakness and related motor disorders

Weakness of limb and respiratory muscles that occurs in the course of critical illness has become an increasingly common and serious complication of adult and pediatric intensive care unit patients and a cause of prolonged ventilatory support, morbidity, and prolonged hospitalization. Two motor disorders that occur singly or together, namely critical illness polyneuropathy and critical illness myopathy, cause weakness of limb and of breathing muscles, making it difficult to be weaned from ventilatory support, commencing rehabilitation, and extending the length of stay in the intensive care unit, with higher rates of morbidity and mortality. Recovery can take weeks or months and in severe cases, and may be incomplete or absent. Recent findings suggest an improved prognosis of critical illness myopathy compared to polyneuropathy. Prevention and treatment are therefore very important. Its management requires an integrated team approach commencing with neurologic consultation, creatine kinase (CK) measurement, detailed electrodiagnostic, respiratory and neuroimaging studies, and potentially muscle biopsy to elucidate the etiopathogenesis of the weakness in the peripheral and/or central nervous system, for which there may be a variety of causes. These tenets of care are being applied to new cases and survivors of the coronavirus-2 disease pandemic of 2019. This chapter provides an update to the understanding and approach to critical illness motor disorders.

Intensive care unit-acquired weakness: Questions the clinician should ask

Intensive care unit (ICU)-acquired weakness (ICU-AW) is defined as clinically detected weakness in critically ill patients in whom there is no plausible etiology other than critical illness. Using electrophysiological methods, patients with ICU-AW are classified in three subcategories: critical illness polyneuropathy, critical illness myopathy and critical illness neuromyopathy. ICU-AW is a frequent complication occurring in critical ill patients. Risk factors include illness severity and organ failure, age, hyperglycemia, parenteral nutrition, drugs and immobility. Due to short- and long-term complications, ICU-AW results in longer hospital stay and increased mortality. Its management is essentially preventive avoiding modifiable risk factors, especially duration of sedation and immobilization that should be as short as possible. Pharmacological approaches have been studied but none have proven efficacy. In the present review, we propose practical questions that the clinician should ask in case of acquired weakness during ICU stay: when to suspect ICU-AW, what risk factors should be identified, how to diagnose ICU-AW, what is the prognosis and how can recovery be improved?

Neurobiology of SARS-CoV-2 interactions with the peripheral nervous system: implications for COVID-19 and pain

SARS-CoV-2 is a novel coronavirus that infects cells through the angiotensin-converting enzyme 2 receptor, aided by proteases that prime the spike protein of the virus to enhance cellular entry. Neuropilin 1 and 2 (NRP1 and NRP2) act as additional viral entry factors. SARS-CoV-2 infection causes COVID-19 disease. There is now strong evidence for neurological impacts of COVID-19, with pain as an important symptom, both in the acute phase of the disease and at later stages that are colloquially referred to as "long COVID." In this narrative review, we discuss how COVID-19 may interact with the peripheral nervous system to cause pain in the early and late stages of the disease. We begin with a review of the state of the science on how viruses cause pain through direct and indirect interactions with nociceptors. We then cover what we currently know about how the unique cytokine profiles of moderate and severe COVID-19 may drive plasticity in nociceptors to promote pain and worsen existing pain states. Finally, we review evidence for direct infection of nociceptors by SARS-CoV-2 and the implications of this potential neurotropism. The state of the science points to multiple potential mechanisms through which COVID-19 could induce changes in nociceptor excitability that would be expected to promote pain, induce neuropathies, and worsen existing pain states.

Evaluation of the Neuropathic Component of Chronic Low Back Pain

OBJECTIVES

Assessment of neuropathic pain in chronic low back syndromes is important. However, there is currently no gold standard for its diagnosis. The aim of this observational cross-sectional study was to assess the neuropathic component of pain in various chronic low back pain syndromes using a range of diagnostic tests.

MATERIALS AND METHODS

Included in this study were 63 patients with chronic axial low back pain (ALBP), 48 patients with chronic radicular syndromes (CRS) comprising 23 with discogenic compression (CDRS) and 25 with lumbar spinal stenosis (LSS), and 74 controls. PainDETECT questionnaire (PDQ), quantitative sensory testing (QST), and skin biopsy with evaluation of intraepidermal nerve fiber density (IENFD) were used to assess the neuropathic pain component.

RESULTS

Positive PDQ (≥19) was obtained more frequently in patients with CDRS and LSS (26.1% and 12.0%, respectively) compared with patients with ALBP (1.6%, P<0.001). The proportion of patients with sensory loss confirmed by QST was lowest in the ALBP subgroup (23.8%) compared with CDRS (47.8%), and LSS (68.0%) subgroups (P<0.001). A reduction in IENFD was disclosed in a proportion of up to 52.0% of affected roots in patients with CRS.

DISCUSSION

Neuropathic pain is quite frequent in CRS, and QST reveals sensory loss as a frequent abnormality in patients with CRS. Using a cut-off value of 19, PDQ identified a neuropathic component in a relatively low proportion of patients with CRS. CRS may be associated with a reduction in IENFD.

Muscle weakness: Understanding the principles of myopathy and neuropathy in the critically ill patient and the management options

Myo-neuropathy of the critically ill patient is a difficult nosological entity to understand and manage. It appears soon after injury, and it is estimated that 20-30% of patients admitted to Intensive Care Units will develop it in some degree. Although muscular and nervous involvement are related, the former has a better prognosis. Myo-neuropathy associates to more morbidity, longer stay in Intensive Care Unit and in hospital, and also to higher costs and mortality. It is considered part of the main determinants of the new entities: the Chronic Critical Patient and the Post Intensive Care Syndrome. This update focuses on aetiology, pathophysiology, diagnosis and strategies that can prevent, alleviate and/or improve muscle (or muscle-nerve) weakness.

Chronic pain in critical care survivors: a narrative review

Chronic pain is an important problem after critical care admission. Estimates of the prevalence of chronic pain in the year after discharge range from 14% to 77% depending on the type of cohort, the tool used to measure pain, and the time point when pain was assessed. The majority of data available come from studies using health-related quality of life tools, although some have included pain-specific tools. Nociceptive, neuropathic, and nociplastic pain can occur in critical care survivors, but limited information about the aetiology, body site, and temporal trajectory of pain is currently available. Older age, pre-existing pain, and medical co-morbidity have been associated with pain after critical care admission. No trials were identified of interventions to target chronic pain in survivors specifically. Larger studies, using pain-specific tools, over an extended follow-up period are required to confirm the prevalence, identify risk factors, explore any association between acute and chronic pain in this setting, determine the underlying pathological mechanisms, and inform the development of future analgesic interventions.

Intensive Care Unit-Acquired Weakness

Intensive care unit-acquired weakness (ICUAW) is a substantial contributor to long-term disability in survivors of critical illness. Critical illness polyneuropathy, critical illness myopathy, and muscle atrophy from disuse contribute in various proportions to ICUAW. ICUAW is a clinical diagnosis supported by electrophysiology and newer diagnostic tests, such as muscle ultrasound. Risk factor reduction, including the aggressive treatment of sepsis and early mobilization, improves outcome. Although some patients with ICUAW experience a full recovery, for others improvement is slow and incomplete and quality of life is adversely affected. This article examines aspects of ICUAW and identifies potential areas of further study.

Erythromelalgia: a cutaneous manifestation of neuropathy?

The low prevalence of erythromelalgia, classified as an orphan disease, poses diagnostic and therapeutic difficulties. The aim of this review is to be an update of the specialized bibliography. Erythromelalgia is an infrequent episodic acrosyndrome affecting mainly both lower limbs symmetrically with the classic triad of erythema, warmth and burning pain. Primary erythromelalgia is an autosomal dominant inherited disorder, while secondary is associated with myeloproliferative diseases, among others. In its etiopathogenesis, there are neural and vascular abnormalities that can be combined. The diagnosis is based on exhaustive clinical history and physical examination. Complications are due to changes in the skin barrier function, ischemia and compromise of cutaneous nerves. Because of the complexity of its pathogenesis, erythromelalgia should always be included in the differential diagnosis of conditions that cause chronic pain and/or peripheral edema. The prevention of crisis is based on a strict control of triggers and promotion of preventive measures. Since there is no specific and effective treatment, control should focus on the underlying disease. However, there are numerous topical and systemic therapies that patients can benefit from.

Chronic intensive care-related pain: Exploratory analysis on predictors and influence on health-related quality of life

BACKGROUND

There is growing evidence for the development of chronic pain after intensive care. Nonetheless, there is only limited knowledge about factors leading to chronic intensive care-related pain (CIRP). Thus, the primary objective was the identification of predictors of CIRP. Moreover, we aimed to assess the impact of CIRP on patients' health-related quality of Life (HRQOL).

METHODS

Comprehensive information on patients' pain before ICU admission and present pain was collected longitudinally by means of the German Pain Questionnaire 6 and 12 months after ICU discharge (ICU_DC ). In addition, a subsample of patients underwent Quantitative Sensory Testing (QST). We used Generalized Estimating Equations to identify predictors of CIRP with logistic regression models.

RESULTS

In total, 204 patients (197/159 at 6/12 months after ICU_DC ) were available for the analyses. In the multivariate models, moderate to severe average pain in the 4 weeks after ICU_DC , lower age, female sex, increased inflammation and chronic pain conditions and increased levels of anxiety before ICU admission were predictive for CIRP. In addition, small fibre deficits and lower disease severity were associated with CIRP in the QST subsample (81 patients, 77/55 at 6/12 months after ICU_DC ). Patients with CIRP reported significantly lower HRQOL than patients without CIRP.

CONCLUSIONS

Chronic intensive care-related pain is associated with specific decrements in HRQOL. Knowledge about the identified predictors is of clinical and scientific importance and might help to reduce the incidence of CIRP.

SIGNIFICANCE

Chronic intensive care-related pain is associated with specific decrements in health-related quality of life. While most of the identified predictors for CIRP can only be considered as risk factors, especially adequate (post-) acute pain management should be studied as preventive strategy.

[Critical illness myopathy and polyneuropathy]

An average of 50-80% of patients treated in the intensive care unit is affected by disturbances of neuromuscular functions due to damage to the nerves and muscles, which has led to the terms critical illness polyneuropathy and myopathy. Both components occur in 30-50% of patients, while the others predominantly show a pure myopathy, while pure neuropathy is rare. Meanwhile, the descriptive term of the concept as intensive care unit-acquired weakness (ICUAW) is preferred. The most significant risk factors for the development of ICUAW are sepsis, multiorgan dysfunction and acute respiratory distress syndrome (ARDS). In at least one third of patients, persistent impairment by paralysis, sensory disturbances and balance problems persist when they leave the ICU. At approximately 10%, these leg-accentuated and highly everyday relevant disorders persist over the first year after ICU therapy. Pure myopathy rarely leads to residual disturbances, while the neuropathic component is responsible for long-term impairments.

Somatosensory Functions in Survivors of Critical Illness

OBJECTIVES

There is growing evidence for increased levels of pain and reduced health-related quality of life in survivors of critical illness. Recent studies showed marked small nerve fiber pathology in critically ill patients, which may contribute to chronic pain states and reduced physical recovery after ICU discharge. Primary objective of this study was the comparison of somatosensory functions between survivors of critical illness 6 months after ICU discharge and controls. In post hoc analyses, we aimed to identify associations between small fiber deficits, pain, health-related quality of life, and clinical data.

DESIGN

Cross-sectional study.

SETTING

Study in critical illness survivors.

PATIENTS

Critical illness survivors (n = 84) and controls (n = 44).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Somatosensory functions were assessed with validated quantitative sensory testing. Pain and pain-related disability were assessed with the chronic pain grade questionnaire. Health-related quality of life was assessed by means of the Short Form-36. Compared with controls, former patients showed significantly increased thermal detection thresholds and more abnormal values in thermal testing, indicating reduced small fiber functioning. In addition, compared to patients without significant small fiber deficits (n = 46, 54.8%), patients with significant small fiber deficits (n = 38, 45.2%) reported higher average pain intensity, pain-related disability, and reduced physical health-related quality of life in the SF-36.

CONCLUSIONS

A large portion of former critically ill patients show small fiber deficits which seem to be associated with increased pain and reduced physical health-related quality of life. Screening of somatosensory functions in the (post-) acute setting could possibly help to identify patients at risk of long-term impairments.

[Critical illness polyneuropathy and myopathy as neurological complications of sepsis]

Intensive care unit acquired weakness (ICUAW) is a frequent and severe complication of intensive care management. Within ICUAW critical illness polyneuropathy (CIP) and myopathy (CIM) can be differentiated. The major symptom of ICUAW is progressive quadriparesis, which makes weaning from the respirator more difficult, can appear early after admission to an ICU and can often be detected several months after discharge from the ICU. The pathophysiology of ICUAW is multifactorial and complex. Potential therapeutic approaches are the early and sufficient therapy of mulitorgan dysfunction, optimal control of glucose levels as well as early and intensive physiotherapy. This review article discusses the data on incidence, pathophysiology, diagnostic approaches and prognosis of ICUAW.

The impairment of small nerve fibers in severe sepsis and septic shock

Background

A decrease of small nerve fibers in skin biopsies during the course of critical illness has been demonstrated recently. However, the diagnostic use of skin biopsies in sepsis and its time course is not known.

Methods

Patients (n=32) with severe sepsis or septic shock were examined using skin biopsies, neurological examination, nerve conduction studies, and sympathetic skin response in the first week after onset of sepsis, 2 weeks and 4 months later and compared to gender- and age-matched healthy controls.

Results

Skin biopsies at the ankle and thigh revealed a significant decrease of intraepidermal nerve fiber density (IENFD) during the first week of sepsis and 2 weeks later. All patients developed critical illness polyneuropathy (CIP) according to electrophysiological criteria and 11 showed IENFD values lower than the 0.05 quantile. Four patients were biopsied after 4 months and still showed decreased IENFD. Results of nerve conduction studies and IENFD did considerably change over time. No differences for survival time between patients with IEFND lower and larger than 3.5 fibers/mm were found.

Conclusions

Skin biopsy is able to detect an impairment of small sensory nerve fibers early in the course of sepsis. However, it may not be suited as a prognostic parameter for survival.

Trial registration

German Clinical Trials Register, DRKS-ID: DRKS00000642, 12/17/2010

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1241-5) contains supplementary material, which is available to authorized users.

Broadening the spectrum of controls for skin biopsy in painful neuropathies: spondylotic cervical myelopathy patients with painful feet

PURPOSE

Intraepidermal nerve fiber density (IENFD) is useful in the evaluation of small-fiber neuropathy (SFN). Recent guidelines recommend extending the spectrum of controls for IENFD assessment by evaluation of patients whose clinical picture mimics that of SFN. The aim of this study was to broaden the spectrum of IENFD controls by the assessment of patients with cervical spondylotic myelopathy (CSM) and painful feet.

METHODS

Evaluation of IENFD from skin biopsy samples and quantitative sensory testing (QST) were performed in a cohort of 14 CSM patients (eight men, median age: 58; range: 46-63 years), with painful feet, exhibiting no clinical or electrophysiological signs of large-fiber polyneuropathy, and no risk factors for peripheral neuropathies.

RESULTS

Quantitative sensory testing abnormalities were found in all but two of the CSM patients (86%), while the IENFD values were within reference range. The mean IENFD value (6.87 ± 2.78 fibers/mm) did not differ from that of an age- and sex-matched cohort of healthy volunteers (7.97 ± 2.21 fibers/mm, P > 0.05).

CONCLUSIONS

The study confirmed normal skin biopsy findings in patients with CSM as one of the clinical conditions mimicking SFN and provided further support for the use of IENFD assessment in case of suspicion of SFN.

Clinical review: intensive care unit acquired weakness

A substantial number of patients admitted to the ICU because of an acute illness, complicated surgery, severe trauma, or burn injury will develop a de novo form of muscle weakness during the ICU stay that is referred to as “intensive care unit acquired weakness” (ICUAW). This ICUAW evoked by critical illness can be due to axonal neuropathy, primary myopathy, or both. Underlying pathophysiological mechanisms comprise microvascular, electrical, metabolic, and bioenergetic alterations, interacting in a complex way and culminating in loss of muscle strength and/or muscle atrophy. ICUAW is typically symmetrical and affects predominantly proximal limb muscles and respiratory muscles, whereas facial and ocular muscles are often spared. The main risk factors for ICUAW include high severity of illness upon admission, sepsis, multiple organ failure, prolonged immobilization, and hyperglycemia, and also older patients have a higher risk. The role of corticosteroids and neuromuscular blocking agents remains unclear. ICUAW is diagnosed in awake and cooperative patients by bedside manual testing of muscle strength and the severity is scored by the Medical Research Council sum score. In cases of atypical clinical presentation or evolution, additional electrophysiological testing may be required for differential diagnosis. The cornerstones of prevention are aggressive treatment of sepsis, early mobilization, preventing hyperglycemia with insulin, and avoiding the use parenteral nutrition during the first week of critical illness. Weak patients clearly have worse acute outcomes and consume more healthcare resources. Recovery usually occurs within weeks or months, although it may be incomplete with weakness persisting up to 2 years after ICU discharge. Prognosis appears compromised when the cause of ICUAW involves critical illness polyneuropathy, whereas isolated critical illness myopathy may have a better prognosis. In addition, ICUAW has shown to contribute to the risk of 1-year mortality. Future research should focus on new preventive and/or therapeutic strategies for this detrimental complication of critical illness and on clarifying how ICUAW contributes to poor longer-term prognosis.