Muscle and nerve biopsies: techniques for the neurologist and neurosurgeon

The multiple roles of nerve biopsy in the diagnosis and prognosis of suspected immune neuropathies

INTRODUCTION

The value of a sural nerve biopsy for the diagnosis of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is controversial. Evidence-based recommendations for its implementation are lacking. We investigated factors leading to biopsy and analyzed biopsy outcomes and consequences, assessed the predictability of biopsy outcomes through clinical parameters to avoid unnecessary biopsies, and compared results with electrophysiological and clinical severity to determine their prognostic value.

METHODS

190 sural nerve biopsies were analyzed in two cohorts. One consisted of 163 biopsies and the second of 72 biopsies from the prospective Immune-mediated Neuropathies Biomaterial and Data registry (INHIBIT). Both have an intersection of 45 patients. 75 data sets from patients without biopsy were used. Analysis of nerve conduction studies, treatment, overall disability sum score (ODSS), biopsy outcomes, and diagnosis was performed.

RESULTS

51% of biopsied patients received the diagnosis CIDP (77% fulfilled EFNS/PNS criteria), 21% were not CIDP typical, and 27% were unspecific. Biopsied patients responded less frequently to immunotherapies at time of biopsy than non-biopsied patients (p = 0.003). Immunotherapy was initiated more frequently after biopsy (p < 0.001) and more often with intravenous immunoglobulins (p < 0.0001). 76% of all biopsied patients met the electrophysiological criteria for CIDP. Sensory nerve action potential amplitudes of 0 µV still provide 73% of histological diagnostic value. Histologic signs of degeneration predicted ODSS worsening after 1 year (p = 0.028) but disease severity did not correlate with histological damage severity.

DISCUSSION

The main indication for nerve biopsy was the treatment of refractory cases of autoimmune neuropathies with the therapeutic consequence of treatment initiation or escalation. Sural biopsy also provided prognostic information. Even with extinguished sural SNAP, the biopsy can still have diagnostic value.

Post-COVID exercise intolerance is associated with capillary alterations and immune dysregulations in skeletal muscles

The SARS-CoV-2 pandemic not only resulted in millions of acute infections worldwide, but also in many cases of post-infectious syndromes, colloquially referred to as "long COVID". Due to the heterogeneous nature of symptoms and scarcity of available tissue samples, little is known about the underlying mechanisms. We present an in-depth analysis of skeletal muscle biopsies obtained from eleven patients suffering from enduring fatigue and post-exertional malaise after an infection with SARS-CoV-2. Compared to two independent historical control cohorts, patients with post-COVID exertion intolerance had fewer capillaries, thicker capillary basement membranes and increased numbers of CD169+ macrophages. SARS-CoV-2 RNA could not be detected in the muscle tissues. In addition, complement system related proteins were more abundant in the serum of patients with PCS, matching observations on the transcriptomic level in the muscle tissue. We hypothesize that the initial viral infection may have caused immune-mediated structural changes of the microvasculature, potentially explaining the exercise-dependent fatigue and muscle pain.

Histological Assessment of Gene Therapy in the Canine DMD Model

Assessing histological changes is essential for characterizing muscle disease progression and for studying the response to therapies in Duchenne muscular dystrophy (DMD), an X-linked progressive muscle-wasting disease caused by the loss of the dystrophin protein. Canine models are by far the best-characterized large animal models for DMD. In this chapter, we describe methods for muscle tissue collection and storage, hematoxylin and eosin staining for studying general muscle morphology, and special staining protocols for evaluating fibrosis, calcification, and neuronal nitric oxide synthase (nNOS) activity. We also provide immunofluorescence staining protocols that are often used to characterize the expression and localization of dystrophin and components of the dystrophin-associated glycoprotein complex. Lastly, we presented immunohistochemical staining protocols that we use to assess muscle inflammation and immune responses.

Techniques for the standard histological and ultrastructural assessment of nerve biopsies

It is always a challenge to acquire a clear picture of the pathological processes and changes in any disease. For this purpose, it is advantageous to directly examine the affected organ. Nerve biopsy has been a method of choice for decades to classify peripheral neuropathies and to find clues to uncover their etiology. The histologic examination of the peripheral nerve provides information on axonal or myelin pathology as well as on the surrounding connective tissue and vascularization of the nerve. Minimal requirements of the workup include paraffin histology as well as resin semithin section histology. Cryostat sections, teased fiber preparations and electron microscopy are potentially useful in a subset of cases. Here we describe our standard procedures for the workup of the tissue sample and provide examples of diagnostically relevant findings.

Mutational and clinical spectrum of centronuclear myopathy in 9 cases and a literature review of Chinese patients

Centronuclear myopathy (CNM) is a group of congenital myopathies with the histopathological findings of centralized nuclei in muscle fibres. In this study, we summarized the mutational spectrum and phenotypic features of nine Chinese patients with CNM and reanalysed the existing data on 32 CNM patients reported in China. In a cohort comprising nine patients, 14 variants were found in three CNM-related genes, including DNM2, RYR1, and TTN, in 4, 3, and 2 patients, respectively. Of the total 14 variants identified, nine were reported, and 5 were novel including one pathogenic, one likely pathogenic, and 3 of undetermined significance (VUS). Pathologically, we identified the percentage of muscle fibres with central nuclei was much higher in the DNM2-related CNM patients than that in other genetic type of CNM. Of the 32 genetic-diagnosed CNM patients previously reported from China, DNM2, MTM1, SPEG, RYR1, and MYH7 mutations accounted for 59.4%, 25.0%, 9.4%, 3.1%, and 3.1%, respectively. Notably, all of the 20 variants of DNM2 were missense mutations, and the missense mutations in exon 8 were found in 60.0% of DNM2 variants. The c.1106G > A/ p.R369Q (NM_001005360) occurred in 26.3% patients of this Chinese cohort with DNM2-CNM. In conclusion, CNM showed a highly variable genetic spectrum, with DNM2 as the most common causative gene in Chinese CNM patients.

[Minimally invasive percutaneous musculoskeletal biopsy performed by Interventional Pathologist for myopathy study. Twenty years of experience]

INTRODUCTION

Muscle biopsy plays a major role in the final diagnosis of myopathies. Open muscle biopsy is the benchmark procedure, although minimally invasive percutaneous muscle biopsy (MIPMB) has demonstrated comparable diagnostic performance at a lower cost and can be carried out by interventional pathologists.

MATERIALS AND METHODS

Muscle biopsies performed from 1997 to 2017 were reviewed and classified according to the type of procedure, whether carried out by an interventional pathologist or another specialist, the diagnosis and the effectiveness of the procedure.

RESULTS

738 muscle biopsies were performed; 32% were open biopsies and 68% MIPMB carried out by pathologist. The muscle most often biopsied was the femoral quadriceps and the most frequent diagnosis was inflammatory myopathies. In only 39 cases (20 open biopsies and 19 MIPMB) was there insufficient tissue for diagnosis.

CONCLUSIONS

Muscle biopsy proved highly effective as a diagnostic tool as 90% yielded adequate tissue samples. The results obtained with MIPMB performed by interventionist pathologists were comparable to those of open muscle biopsy.

A well-tolerated core needle muscle biopsy process suitable for children and adults

Serial muscle biopsies within clinical trials for Duchenne muscular dystrophy (DMD) are critical to document therapeutic responses. Less invasive means of sampling muscle are needed. We analyzed a retrospective consecutive case-series cohort of vacuum-assisted core needle muscle biopsy procedures performed on healthy and dystrophic individuals at a single institution assessing for safety and reliability of obtaining sufficient high-quality biopsy tissue for histologic assessment in adult and pediatric subjects. Of 471 muscle cores from 128 biopsy procedures, 377-550 mg of total muscle tissue was obtained per procedure with mean core weight of 129 mg (SD, 25.1 mg). All biopsies were adequate for histological assessment. There were no significant adverse events. This core needle biopsy approach, when combined with improved sample processing, provides a safe means to consistently obtain muscle samples for diagnostic and clinical trial applications.

The spectrum of muscle pathologies: Three decades of experience from a reference laboratory in Saudi Arabia

BACKGROUND

When investigating patients with a suspected neuromuscular disorder, a muscle biopsy is considered an instrumental tool to reach a definitive diagnosis. There is a paucity of publications that assess the diagnostic utilization and yield of muscle biopsies. We intend to present our experience in this regard over an extended period of more than three decades.

METHODS

This is an observational retrospective cohort study in which we collected pathology reports for muscle biopsies diagnosed at our reference lab between 1986 and 2017.

RESULTS

We identified a total of 461 cases of muscle biopsy performed, which fulfilled the inclusion criteria. Pediatric cases defined as ≤14 years of age constituted a significant proportion of cases (n = 275, 60%). Normal biopsies were reported in 27% of cases (n = 124), and in 4%, the biopsies were non-diagnostic. The most common pathologies reported were non-specific myopathy (n = 72, 16%), dystrophy (n = 71, 15%), and neurogenic disorders (n = 60, 13%).

CONCLUSION

In conclusion, the muscle biopsy will continue to play a crucial role, as a gold standard or as a complementary investigation, in the diagnosis of certain neuromuscular disorders. Increasing the yield and accuracy of muscle pathology should be the main concern and priority to neuropathologists reporting muscle biopsies. In addition, utilizing next-generation sequencing and other molecular techniques have changed the location of muscle biopsy in the algorithm of the diagnosis of neuromuscular disorders. This paper is an urgent call to establish the Saudi Neuropathology Society and the muscle pathology and neuromuscular disorders registry.

Mutational and clinical spectrum in a cohort of Chinese patients with hereditary nemaline myopathy

Hereditary nemaline myopathy (NM) is one of the most common congenital myopathies with the histopathological findings of nemaline bodies. We used targeted next-generation sequencing to identify causative mutations in 48 NM patients with confirmed myopathological diagnosis, analyze the mutational spectrum and phenotypic features. Furthermore, reverse transcription polymerase chain reaction (RT-PCR) was used to confirm the pathogenic effect of one nebulin (NEB) splicing variant. The results showed that variants were found in five NM-associated genes, including NEB, actin alpha 1 (ACTA1), troponin T1, Kelch repeat and BTB domain-containing 13, and cofilin-2, in 34 (73.9%), 7 (15.2%), 3 (6.5%), 1 (2.2%), and 1 (2.2%) patients, respectively, in a total of 46/48 (95.8%) NM patients. Of the total 64 variants identified, 51 were novel variants including 26 pathogenic, 1 probably pathogenic, and 24 variant of uncertain significance (VUS). Notably, one NEB splicing mutation, c.21417+3A>G causing exon 144 splicing (NM_001164508.1), as confirmed by RT-PCR, was found in 52.9% (18 patients) of NEB variant-carrying patients. Typical congenital NM, the most common clinical subtype (60.4%), was associated with five NM genes. We concluded that hereditary NM showed a highly variable genetic spectrum. NEB was the most frequent causative gene in this Chinese cohort, followed by ACTA1. We found a hotspot splicing mutation in NEB among Chinese cohort.

Intensive Care Management of the Neuromuscular Patient

Neuromuscular emergencies are a distinct group of acute neurological diseases with distinct characteristic presentations. Patients who suffer from this group of diseases are at immediate risk of losing protection of their native airway as well as aspirating orogastric contents. This is secondary to weakness of the muscles of the oropharynx and respiratory muscles. Although some neuromuscular emergencies such as myasthenia gravis or Guillain-Barré syndrome are well understood, others such as critical illness myopathy and neuropathy are less well characterized. In this chapter, we have discussed the pathophysiology, diagnostic evaluation, and management options in patients who are admitted to the intensive care unit. We have also emphasized the importance of a thorough understanding of the use of pharmacological anesthetic agents in this patient population.

The Role of Electrodiagnostic Testing, Imaging, and Muscle Biopsy in the Investigation of Muscle Disease

PURPOSE OF REVIEW

This article reviews the roles of electrodiagnostic testing, imaging studies (MRI and ultrasound), and muscle biopsy in evaluating patients for possible muscle diseases.

RECENT FINDINGS

In addition to electrodiagnostic testing and muscle biopsy, muscle imaging is increasingly being used in the evaluation of patients with suspected muscle disease. MRI and ultrasound can help identify patterns of muscle involvement that may narrow the differential diagnosis and guide further testing. In addition, imaging can identify potential targets for muscle biopsy and can help evaluate for and exclude certain conditions that may mimic muscle disease.

SUMMARY

This article provides a comprehensive overview of various testing modalities used in the evaluation of patients with suspected muscle disease, including electrodiagnostic studies, muscle imaging, and biopsy. In combination with a thorough history and clinical examination, these modalities can help narrow the differential diagnosis or, in certain cases, can confirm a specific etiology of muscle disease.