Neuromuscular Pathology Made Easy

Maher Kurdi, Maher Kurdi

• Publisher: CRC Press
• Year: 2021
• ISBN:
  9781000346558
• Edition: 1
• Topic: Medicine
• Subtopic: Pathology

The scope of Neuromuscular Pathology continuous to expand, as evidenced by the numerous multivolume and speciality texts published in recent years. This short textbook provides a complete overview of both clinical and histological aspects of common and rare neuromuscular diseases. The objective is twofold: to provide information about neuromuscular diseases in a simplified, integrated, and rapidly accessible format suited to those initially encountering the discipline, and also to provide a clear approach using simple pictures, tables and algorithms to illustrate histological features in muscle and nerve biopsy.

This volume is conveniently divided into three sections with a total of 30 chapters. The first section deals with basic principles of neuromuscular histology and physiology, processing technique, histochemistry, and laboratory management. The second and third sections deal with neuromuscular diseases that are summarized in a stepwise approach, complemented by algorithms and organized tables.

• A simplified, integrated, and rapidly accessible format covering both common and rare neuromuscular diseases

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• Clear simple illustrations, organized tables and algorithms to aid the reader in finding an easy approach to accurate diagnosis

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• Practical tips to facilitate histopathological diagnosis.

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• Clinical scenarios discussing common neuromuscular conditions

Neurologists, neuropathologists, trainees and medical students involved in clinical neuroscience and pathology will find this guide of practical benefit in both education and practice.

Part I

General

Chapter 1
Muscle and Nerve Histology

Contents

1. 1.1 Muscle Histology
   • 1.1.1 Mitochondria
2. 1.2. Peripheral Nerve Histology

1.1Muscle Histology

Muscle tissue is differentiated into smooth, cardiac, and skeletal muscles. This differentiation embryonically starts to develop from mesoderm during the 7^th week of gestation and it completely forms by the 28^th week of gestation. The nuclei take their peripheral positions after 20 weeks of gestation. Skeletal muscle is elongated on longitudinal sections and striated in cross section. The entire portion is enclosed in a connective tissue sheath called epimysium, which is composed of extracellular matrix and irregular collagens. The epimysium connects into the tendon sheath and divides the muscle into groups of bundles, or fascicles, separated from each other by perimysium (Figure 1.1). The myotendinous junction area sometimes mimics dystrophy (pseudomyopathy), as it may show alternative features of hypertrophic and atrophic fibers, excess fibrous tissue, and multiple internal nuclei (Figure 1.2).

Figure 1.1(a) An illustrated photograph of skeletal muscle layers. (b) Cross section of normal skeletal muscle shows the muscle fibers within the fascicles. (H&E ×20.)

Figure 1.2Myotendinous junction with hypertrophic and atrophic fibers, multiple internal nuclei, and increased connective tissue. (H&E ×40.)

Each group of muscle fascicles is composed of uniform muscle fibers called myocytes. They are separated from each other by a network of reticular fibers and extracellular matrix, called endomysium.

Each muscle fiber contains either a single nucleus or multiple nuclei and a cytoplasm called sarcoplasm, and it is surrounded by a plasma membrane called sarcolemma. The nuclei are usually peripherally located, heterochromatic, and containing fine nucleoli and stippled nucleoplasm. They stain blue with hematoxylin and red with Gomori trichrome. Centrally positioned nuclei for more than 3% of a whole fascicle is considered abnormal.

The sarcoplasm contains multiple organelles including mitochondria, sarcoplasmic reticulum, Golgi apparatus, microtubules, glycogens, ribosomes, lipid droplets, and myofibrils. The mitochondria are located at the level of the I-band. They present in type I fibers more than type II fibers, but this is not considered a consistent distinguishing feature.

The sarcolemma consists of an inner plasma membrane (plasmalemma) and outer membrane (external basal lamina). The plasmalemma is an excitable membrane composed of a lipid bilayer and a variety of ion channels and proteins present on the cytoskeleton. Some of these sarcolemmal proteins are summarized in Table. 1.1 and Figure 1.3.

Table 1.1 Intracellular and extracellular sarcolemmal proteins associated with each muscle fiber.

Protein	Structure	Interaction site
Dystrophin	Sarcolemmal protein with four domains (actin-binding, central rod, carboxyl terminus, cysteine-rich domain)	Sarcoglycan, dystroglycan syntrophin, dystrobrevin
Sarcoglycan	Transmembrane protein that has four subtypes: α, β, γ, δ	Dystrophin, filamin-C
Dystroglycan	Transmembrane protein (α, β). α-II laminin (merosin)	Dystrophin, caveolin-3
Dysferlin	Type II transmembrane protein	Caveolin-3
Caveolin-3	Protein found in caveolae	Dysferlin, RYR1
Myotilin	Sarcomeric Z-disc protein	Filamin-C, α-actinin
Emerin	Nuclear membrane protein anchored to cytoskeleton	Actin, lamin A/C, CTNNB1
Abbreviations: RYR1: ryanodine receptor 1; CTNNB1: catenin beta-1 protein. Note: The interaction site is the binding site where each protein interacts with another one.

Figure 1.3(Left) A diagram of sarcolemmal muscle proteins. (Right) Groups of important muscle proteins: (a) dystrophin; (b) sarcoglycan; (c) dysferlin; (d) emerin (×40). This figure was created with Biorender.com.

The plasmalemma extends deeps into the muscle fibers, forming T-tubules that carry the depolarization of action potential inside the fibers. Hence, a T-tubule with two terminal cisterns forms a triad. The triad has a voltage-gated calcium channel and ryanodine receptor. T-tubules and sarcoplasmic reticulum are essential components involved in muscle contractio...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents
• List of Contributors
• Preface
• Acknowledgments
• Abbreviations
• Part I General
• Part II Muscle
• Part III Nerve
• Index