Infectious neuropathies

Small fiber neuropathy

Small fiber neuropathy (SFN) is a condition involving the small nerve fibers of the peripheral nervous system, specifically the thinly myelinated Aδ and unmyelinated C fibers. It is an increasingly acknowledged condition within the spectrum of neuropathic pain disorders, leading to a rise in diagnosed patients. SFN is characterized by neuropathic pain, that is often described as burning, and typically presents in the hands and feet ascending proximally. Since small nerve fibers are involved in the autonomic nervous system, SFN can also lead to autonomic dysfunction. In the clinical setting, SFN diagnosis is frequently based on the Besta Criteria, which include skin biopsy and quantitative sensory testing. For clinical trials, the ACTTION criteria are also recommended. However, the diagnostic process is often complex, prompting research towards more accessible diagnostic methods. The pathophysiology of SFN remains unclear, thereby challenging therapeutic strategies. A large variety of underlying conditions has been associated with SFN, including metabolic, immune-mediated, infectious, toxic and hereditary conditions. The discovery of genetic sodium channelopathies in SFN provides insight into its underlying mechanisms. Newly discovered mutations within these genes reveal that SFN often shows overlapping clinical presentations with other sodium channelopathies. This chapter provides an in-depth look at SFN, including its clinical features, diagnostic methods, underlying conditions and possible therapeutic strategies.

Neurological features of Hansen disease: a retrospective, multicenter cohort study

To elucidate the neurological features of Hansen disease. The medical records of patients with confirmed Hansen disease transferred from the neurology department were reviewed, and all medical and neurological manifestations of Hansen disease were assessed. Eleven patients with confirmed Hansen disease, 10 with newly detected Hansen disease and 1 with relapsed Hansen disease, who visited neurology departments were enrolled. The newly detected patients with Hansen disease were classified as having lepromatous leprosy (LL, n = 1), borderline lepromatous leprosy (BL, n = 2), borderline leprosy (BB, n = 2), borderline tuberculoid leprosy (BT, n = 1), tuberculoid leprosy (TT, n = 2), or pure neural leprosy (PNL, n = 2). All of the patients with confirmed Hansen were diagnosed with peripheral neuropathy (100.00%, 11/11). The symptoms and signs presented were mainly limb numbness (100.00%, 11/11), sensory and motor dysfunction (100.00%, 11/11), decreased muscle strength (90.90%, 10/11), and skin lesions (81.81%, 9/11). Nerve morphological features in nerve ultrasonography (US) included peripheral nerve asymmetry and segmental thickening (100.00%, 9/9). For neuro-electrophysiology feature, the frequency of no response of sensory nerves was significantly higher than those of motor nerves [(51.21% 42/82) vs (24.70%, 21/85)(P = 0.0183*)] by electrodiagnostic (EDX) studies. Nerve histological features in nerve biopsy analysis included demyelination (100.00%, 5/5) and axonal damage (60.00%, 3/5). In addition to confirmed diagnoses by acid-fast bacteria (AFB) staining (54.54%, 6/11) and skin pathology analysis (100.00%, 8/8), serology and molecular technology were positive in 36.36% (4/11) and 100.00% (11/11) of confirmed patients of Hansen disease, respectively. It is not uncommon for patients of Hansen disease to visit neurology departments due to peripheral neuropathy. The main pathological features of affected nerves are demyelination and axonal damage. The combination of nerve US, EDX studies, nerve biopsy, and serological and molecular tests can improve the diagnosis of Hansen disease.

Neuralgic Amyotrophy and Hourglass Nerve Constriction/Nerve Torsion: Two Sides of the Same Coin? A Clinical Review

Neuralgic amyotrophy, also called Parsonage-Turner syndrome, in its classic presentation is a brachial plexopathy or a multifocal neuropathy, involving mainly motor nerves of the upper limb with a monophasic course. Recently, a new radiological entity was described, the hourglass constriction, which is characterized by a very focal constriction of a nerve, or part of it, usually associated with nerve thickening proximally and distally to the constriction. Another condition, which is similar from a radiological point of view to hourglass constriction, is nerve torsion. The pathophysiology of neuralgic amyotrophy, hourglass constriction and nerve torsion is still poorly understood, and a generic role of inflammation is proposed for all these conditions. It is now widely accepted that nerve imaging is necessary in identifying hourglass constrictions/nerve torsion pre-surgically in patients with an acute mononeuropathy/plexopathy. Ultrasound and MRI are useful tools for diagnosis, and they are consistent with intraoperative findings. The prognosis is generally favorable after surgery, with a high rate of good motor recovery.

Imaging of Nerve Disorders in the Elbow

Neuropathies of the elbow represent a spectrum of disorders that involve more frequently the ulnar, radial, and median nerves. Reported multiple pathogenic factors include mechanical compression, trauma, inflammatory conditions, infections, as well as tumor-like and neoplastic processes. A thorough understanding of the anatomy of these peripheral nerves is crucial because clinical symptoms and imaging findings depend on which components of the affected nerve are involved. Correlating clinical history with the imaging manifestations of these disorders requires familiarity across all diagnostic modalities. This understanding allows for a targeted imaging work-up that can lead to a prompt and accurate diagnosis.

The Interplay Between Neuroinfections, the Immune System and Neurological Disorders: A Focus on Africa

Neurological disorders related to neuroinfections are highly prevalent in Sub-Saharan Africa (SSA), constituting a major cause of disability and economic burden for patients and society. These include epilepsy, dementia, motor neuron diseases, headache disorders, sleep disorders, and peripheral neuropathy. The highest prevalence of human immunodeficiency virus (HIV) is in SSA. Consequently, there is a high prevalence of neurological disorders associated with HIV infection such as HIV-associated neurocognitive disorders, motor disorders, chronic headaches, and peripheral neuropathy in the region. The pathogenesis of these neurological disorders involves the direct role of the virus, some antiretroviral treatments, and the dysregulated immune system. Furthermore, the high prevalence of epilepsy in SSA (mainly due to perinatal causes) is exacerbated by infections such as toxoplasmosis, neurocysticercosis, onchocerciasis, malaria, bacterial meningitis, tuberculosis, and the immune reactions they elicit. Sleep disorders are another common problem in the region and have been associated with infectious diseases such as human African trypanosomiasis and HIV and involve the activation of the immune system. While most headache disorders are due to benign primary headaches, some secondary headaches are caused by infections (meningitis, encephalitis, brain abscess). HIV and neurosyphilis, both common in SSA, can trigger long-standing immune activation in the central nervous system (CNS) potentially resulting in dementia. Despite the progress achieved in preventing diseases from the poliovirus and retroviruses, these microbes may cause motor neuron diseases in SSA. The immune mechanisms involved in these neurological disorders include increased cytokine levels, immune cells infiltration into the CNS, and autoantibodies. This review focuses on the major neurological disorders relevant to Africa and neuroinfections highly prevalent in SSA, describes the interplay between neuroinfections, immune system, neuroinflammation, and neurological disorders, and how understanding this can be exploited for the development of novel diagnostics and therapeutics for improved patient care.

Approach to Neuropathic Pain

Neuropathic pain is a common chief complaint encountered by neurologists and primary care providers. It is caused by disorders involving the somatosensory nervous system. The clinical evaluation of neuropathic pain is challenging and requires a multifaceted systematic approach with an emphasis on a thorough history and physical examination to identify characteristic signs and symptoms. Ancillary laboratory investigations, targeted imaging, and electrodiagnostic studies further help identify underlying etiologies to guide specific treatments. Management of neuropathic pain encompasses treating the underlying pathology as well as symptomatic control with nonpharmacological, pharmacological, and interventional therapies. Here, we present an approach to help evaluate patients with neuropathic pain.

Common Peroneal Nerve Injury in a Patient with COVID-19 Infection

This report described a 46-year man with the characteristic Computerized Tomography (CT) scan findings of Corona Virus Disease Infection 19 (COVID-19) who presented to the hospital with right ankle weakness three weeks after the pneumonitis. He had been initially hospitalized, complaining of fever, myalgia, cough, and dyspnea. Electromyogram (EMG) revealed obvious evidence of increased insertional activity (IA) and significant denervation potentials, including positive sharp waves (PSW) and fibrillation potentials, particularly in ankle dorsiflexor muscles. Moreover, no voluntary motor unit action potential (MUAP) was observed. Eventually, the patient was diagnosed with severe axonal mononeuropathy of the right CPN, which could be considered a rare complication of COVID-19.

Immune-mediated vincristine-induced neuropathy: Unlocking therapies

Vincristine-induced peripheral neuropathy (VIPN) is a prevalent and painful complication in cancer patients that lacks effective treatments. In this issue of JEM, Starobova et al. (2021. J. Exp. Med.https://doi.org/10.1084/jem.20201452) report that VIPN is driven by innate immune system activation, a discovery that unlocks immunotherapies as potential treatments.

Imaging Review of Peripheral Nerve Injuries in Patients with COVID-19

With surging numbers of patients with coronavirus disease 2019 (COVID-19) throughout the world, neuromuscular complications and rehabilitation concerns are becoming more apparent. Peripheral nerve injury can occur in patients with COVID-19 secondary to postinfectious inflammatory neuropathy, prone positioning-related stretch and/or compression injury, systemic neuropathy, or nerve entrapment from hematoma. Imaging of peripheral nerves in patients with COVID-19 may help to characterize nerve abnormality, to identify site and severity of nerve damage, and to potentially elucidate mechanisms of injury, thereby aiding the medical diagnosis and decision-making process. This review article aims to provide a first comprehensive summary of the current knowledge of COVID-19 and peripheral nerve imaging.

Laboratory Tests for Neuropathies: What to do and to Avoid

OBJECTIVES

laboratory tests for work-up of hereditary and acquired neuropathies of peripheral nerves are frequently uncritically utilized. This overview focuses on the most common laboratory tests and investigations needed for diagnosing PNPs by the general neurologist.

METHOD

Literature search.

RESULTS

laboratory tests recommended for the work-up of hereditary and acquired neuropathies should be chosen according to the individual and family history, clinical presentation, and electrophysiological findings. Laboratory tests should be selected specifically according to the suspected type of neuropathy to avoid unnecessary tests and expenses. Work-up should include as few samples as necessary for uncovering the etiology and should consider the sensitivity/specificity of the tests applied.. Basic screening tests for neuropathies should include a blood cell count, thyroid, renal and liver function tests, blood glucose levels, HbA1c, vitamin-B12, and immunofixation. Other laboratory investigations should be carried out only if a specific phenotype is present or if unexpected changes of the disease course occur. In these cases referral to a neuromuscular center is recommended.

CONCLUSIONS

Laboratory tests are helpful for the diagnosis of acquired and hereditary neuropathies but these tests should be ordered according to the history, clinical presentation and findings on electrophysiological investigations. If basic laboratory parameters fail to uncover the etiology, patients should be referred to a center specialized in neuromuscular disorders.

Infections of the Nervous System

Microorganisms can affect the entire neuraxis, producing a variety of neurologic complications that frequently entail prolonged hospitalizations and complicated treatment regimens. The spread of pathogens to new regions and the reemergence of opportunistic organisms in immunocompromised patients pose increasing challenges to health care professionals. Because rapid diagnosis and treatment may prevent long-term neurologic sequelae, providers should approach these diseases with a structured, neuroanatomic framework, incorporating a thorough history, examination, laboratory analysis, and neuroimaging in their clinical reasoning and decision-making.

HCV RNA Genomic sequences and HCV-E2 glycoprotein in sural nerve biopsies from HCV-infected patients with peripheral neuropathy

AIMS

Peripheral neuropathy (PN), the major neurological complication of chronic HCV infection, is frequently associated with mixed cryoglobulinaemia (MC) and small-vessel systemic vasculitis. While humoral and cell-mediated immune mechanisms are suspected to act together in an aberrant immune response that results in peripheral nerve damage, the role of HCV remains largely speculative. The possible demonstration of HCV in peripheral nerve tissue would obviously assume important pathogenic implications.

METHODS

We studied sural nerve biopsies from 11 HCV-positive patients with neuropathic symptoms: five with and six without MC. In situ hybridization (ISH) and immunofluorescence studies were carried out to detect genomic and antigenomic HCV RNA sequences and HCV-encoded E2-glycoprotein, respectively.

RESULTS

Epineurial vascular deposits of E2-glycoprotein were found in four (80%) MC and in two (33.3%) non-MC patients, respectively. These findings were enhanced by the perivascular deposition of positive-, though not negative-strand replicative RNA, as also found in the nerve extracts of all patients. Mild inflammatory cell infiltrates with no deposits of immunoglobulins and/or complement proteins were revealed around small vessels, without distinct vasculitis changes between MC and non-MC patients.

CONCLUSIONS

These results indicate that nerve vascular HCV RNA/E2 deposits associated to perivascular inflammatory infiltrates were similar in chronically HCV-infected patients, regardless of cryoglobulin occurrence. Given the failure to demonstrate HCV productive infection in the examined sural nerve biopsies, nerve damage is likely to result from virus-triggered immune-mediated mechanisms.

The role of primary infection of Schwann cells in the aetiology of infective inflammatory neuropathies

Numerous different pathogens are responsible for infective peripheral neuropathies and this is generally the result of the indirect effects of pathogen infection, namely anti pathogen antibodies cross reacting with epitopes on peripheral nerve, auto reactive T cells attacking myelin, circulating immune complexes and complement fixation. Primary infection of Schwann cells (SC) associated with peripheral nerve inflammation is rare requiring pathogens to cross the Blood Peripheral Nerve Barrier (BPNB) evade anti-pathogen innate immune pathways and invade the SC. Spirochetes Borrelia bourgdorferi and Trepomema pallidum are highly invasive, express surface lipo proteins, but despite this SC are rarely infected. However, Trypanosoma cruzi (Chaga's disease) and Mycobacterium leprae. Leprosy are two important causes of peripheral nerve infection and both demonstrate primary infection of SC. This is due to two novel strategies; T. cruzi express a trans-silalidase that mimics host neurotrophic factors and infects SC via tyrosine kinase receptors. M. leprae demonstrates multi receptor SC tropism and subsequent infection promotes nuclear reprogramming and dedifferentiation of host SC into progenitor stem like cells (pSLC) that are vulnerable to M. leprae infection. These two novel pathogen evasion strategies, involving stem cells and receptor mimicry, provide potential therapeutic targets relevant to the prevention of peripheral nerve inflammation by inhibiting primary SC infection.

Virus Infections Incite Pain Hypersensitivity by Inducing Indoleamine 2,3 Dioxygenase

Increased pain sensitivity is a comorbidity associated with many clinical diseases, though the underlying causes are poorly understood. Recently, chronic pain hypersensitivity in rodents treated to induce chronic inflammation in peripheral tissues was linked to enhanced tryptophan catabolism in brain mediated by indoleamine 2,3 dioxygenase (IDO). Here we show that acute influenza A virus (IAV) and chronic murine leukemia retrovirus (MuLV) infections, which stimulate robust IDO expression in lungs and lymphoid tissues, induced acute or chronic pain hypersensitivity, respectively. In contrast, virus-induced pain hypersensitivity did not manifest in mice lacking intact IDO1 genes. Spleen IDO activity increased markedly as MuLV infections progressed, while IDO1 expression was not elevated significantly in brain or spinal cord (CNS) tissues. Moreover, kynurenine (Kyn), a tryptophan catabolite made by cells expressing IDO, incited pain hypersensitivity in uninfected IDO1-deficient mice and Kyn potentiated pain hypersensitivity due to MuLV infection. MuLV infection stimulated selective IDO expression by a discreet population of spleen cells expressing both B cell (CD19) and dendritic cell (CD11c) markers (CD19+ DCs). CD19+ DCs were more susceptible to MuLV infection than B cells or conventional (CD19neg) DCs, proliferated faster than B cells from early stages of MuLV infection and exhibited mature antigen presenting cell (APC) phenotypes, unlike conventional (CD19neg) DCs. Moreover, interactions with CD4 T cells were necessary to sustain functional IDO expression by CD19+ DCs in vitro and in vivo. Splenocytes from MuLV-infected IDO1-sufficient mice induced pain hypersensitivity in uninfected IDO1-deficient recipient mice, while selective in vivo depletion of DCs alleviated pain hypersensitivity in MuLV-infected IDO1-sufficient mice and led to rapid reduction in splenomegaly, a hallmark of MuLV immune pathogenesis. These findings reveal critical roles for CD19+ DCs expressing IDO in host responses to MuLV infection that enhance pain hypersensitivity and cause immune pathology. Collectively, our findings support the hypothesis elevated IDO activity in non-CNS due to virus infections causes pain hypersensitivity mediated by Kyn. Previously unappreciated links between host immune responses to virus infections and pain sensitivity suggest that IDO inhibitors may alleviate heightened pain sensitivity during infections.

M. leprae components induce nerve damage by complement activation: identification of lipoarabinomannan as the dominant complement activator

Peripheral nerve damage is the hallmark of leprosy pathology but its etiology is unclear. We previously identified the membrane attack complex (MAC) of the complement system as a key determinant of post-traumatic nerve damage and demonstrated that its inhibition is neuroprotective. Here, we determined the contribution of the MAC to nerve damage caused by Mycobacterium leprae and its components in mouse. Furthermore, we studied the association between MAC and the key M. leprae component lipoarabinomannan (LAM) in nerve biopsies of leprosy patients. Intraneural injections of M. leprae sonicate induced MAC deposition and pathological changes in the mouse nerve, whereas MAC inhibition preserved myelin and axons. Complement activation occurred mainly via the lectin pathway and the principal activator was LAM. In leprosy nerves, the extent of LAM and MAC immunoreactivity was robust and significantly higher in multibacillary compared to paucibacillary donors (p = 0.01 and p = 0.001, respectively), with a highly significant association between LAM and MAC in the diseased samples (r = 0.9601, p = 0.0001). Further, MAC co-localized with LAM on axons, pointing to a role for this M. leprae antigen in complement activation and nerve damage in leprosy. Our findings demonstrate that MAC contributes to nerve damage in a model of M. leprae-induced nerve injury and its inhibition is neuroprotective. In addition, our data identified LAM as the key pathogen associated molecule that activates complement and causes nerve damage. Taken together our data imply an important role of complement in nerve damage in leprosy and may inform the development of novel therapeutics for patients.

Oleo gum resin of Ferula assa-foetida L. ameliorates peripheral neuropathy in mice

ETHNOPHARMACOLOGICAL RELEVANCE

According to the Chinese, European, Iranian and Indian traditional medicines, oleo gum resin of Ferula assa-foetida (asafoetida) has therapeutic effects on different kinds of diseases. Some of these effects are related to the diseases of nervous system such as hysteresis and convulsion. In recent studies, some anti-epileptic and neuroprotective roles were also considered for it and we examined its possible role on treatment of peripheral neuropathy.

MATERIAL AND METHODS

in vitro studies were carried out to identify the response of isolated sciatic nerves to different concentrations of oleo gum resin of asafoetida solved in Lock׳s solution. Then, in vivo studies were conducted to evaluate its effect on amelioration of peripheral neuropathy in mice. Peripheral neuropathy was induced by intraperiotoneal injection of high doses of pyridoxine in adult Balb/c male mice. Tail flick tests were performed to identify the incidence of neuropathy in animals. After 10 days treatment with asafoetida, the efficiency of treatment was assessed by behavioral, electrophysiological and histological studies.

RESULTS

in vitro experiments confirmed that incubating the nerves in aqueous extract of oleo gum rein of asafoetida increased the amplitude and decreased the latent period of nerve compound action potential (CAP). Nerve conduction velocity (NCV) and amplitude of CAP also improved in asafoetida treated animals. Histological and behavioral studies showed that asafoetida was able to facilitate the healing process in peripheral nerves.

CONCLUSIONS

in vitro experiments showed that asafoetida is a nerve stimulant and its administration in neuropathic mice exerted neuroprotecting effects through stimulating axonal regeneration and remyelination and decrement of lymphocyte infiltration.

Neuropathic cancer pain: What we are dealing with? How to manage it?

Cancer pain is a serious health problem, and imposes a great burden on the lives of patients and their families. Pain can be associated with delay in treatment, denial of treatment, or failure of treatment. If the pain is not treated properly it may impair the quality of life. Neuropathic cancer pain (NCP) is one of the most complex phenomena among cancer pain syndromes. NCP may result from direct damage to nerves due to acute diagnostic/therapeutic interventions. Chronic NCP is the result of treatment complications or malignancy itself. Although the reason for pain is different in NCP and noncancer neuropathic pain, the pathophysiologic mechanisms are similar. Data regarding neuropathic pain are primarily obtained from neuropathic pain studies. Evidence pertaining to NCP is limited. NCP due to chemotherapeutic toxicity is a major problem for physicians. In the past two decades, there have been efforts to standardize NCP treatment in order to provide better medical service. Opioids are the mainstay of cancer pain treatment; however, a new group of therapeutics called coanalgesic drugs has been introduced to pain treatment. These coanalgesics include gabapentinoids (gabapentin, pregabalin), antidepressants (tricyclic antidepressants, duloxetine, and venlafaxine), corticosteroids, bisphosphonates, N-methyl-D-aspartate antagonists, and cannabinoids. Pain can be encountered throughout every step of cancer treatment, and thus all practicing oncologists must be capable of assessing pain, know the possible underlying pathophysiology, and manage it appropriately. The purpose of this review is to discuss neuropathic pain and NCP in detail, the relevance of this topic, clinical features, possible pathology, and treatments of NCP.