You’re Reading a Preview Become a Clinical Tree membership for Full access and enjoy Unlimited articles Become membership If you are a member. Log in here

You’re Reading a Preview Become a Clinical Tree membership for Full access and enjoy Unlimited articles Become membership If you are a member. Log in here

In addition to the many inherited disorders already described in this book, nerves and muscles can be affected by a wide range of drugs and toxins. Some drug-related myopathies, such as those caused by statins, steroids and alcohol, are common, while others are very rare. The widespread use of statins has resulted in these drugs becoming the commonest defined cause of myalgia and hyperCKaemia in clinical…

There is a large and heterogeneous group of acquired disorders that have been grouped together collectively as inflammatory muscle diseases. Common clinical diagnoses are polymyositis, dermatomyositis and inclusion body myositis. An emerging group are myopathies without much evidence of inflammation but with autoimmune aetiology: immune-mediated necrotizing myopathy (IMNM) or necrotizing autoimmune myopathy (NAM). Muscle inflammation with non-specific features is also frequently encountered in other autoimmune disorders…

There have been major advances in the understanding of the underlying causes of the various myasthenic syndromes, all of which involve abnormalities related to the neuromuscular junction ( Fig. 21.1 ). Their characteristic feature is muscle weakness with fatigue. Myasthenia gravis is an acquired autoimmune disorder caused in most cases by antibodies to the acetylcholine receptors (AChRs), or to a tyrosine kinase receptor, muscle-specific kinase (MuSK),…

Action potentials in muscle, initiated by depolarization by a nerve impulse and depolarization of the muscle fibre, require the rapid movement of inorganic ions through transmembrane ion channels. The action potential results in the release of calcium ions from the sarcoplasmic reticulum (SR), leading to contraction of the myofibrils. These events of action potential to contraction of muscle fibres are known as excitation–contraction coupling ( ).…

In addition to inherited or acquired neuromuscular disorders, muscle weakness and alterations in muscle bulk can occur in association with several underlying conditions and as a consequence of ageing. Hormone imbalances, vitamin deficiencies, malignancies and ageing are the most common causes, and, although the muscle pathology is often non-specific, the pathologist should be aware of their effects. Endocrine Disorders Many hormones have an important role in…

Skeletal muscles not only use glycogen but also lipid as a source of energy. The oxidation of lipids occurs in the mitochondria and involves a series of enzymatic reactions ( Fig. 18.1a, b ). Defects in these pathways and in the pathways of oxidative phosphorylation in the mitochondria lead to a heterogeneous group of muscle disorders. Open full size image Fig. 18.1a Schematic representation of muscle…

There has been a dramatic increase in the understanding of disorders that affect the metabolism of muscle, particularly with regard to their biochemistry and molecular basis. A large number of clinical syndromes related to glycogen and lipid metabolism, mitochondrial function and ion channels are now known but only in some is muscle pathology helpful. In the following chapters we shall concentrate on conditions where pathological studies…

Introduction A vacuole is a membrane-bound area of a muscle fibre that may contain various cellular components or enzymes. The type and function of a vacuole vary, and the properties of a vacuole can be a useful pathological indicator. The membrane may be revealed with antibodies to sarcolemmal proteins, or may only be visible with electron microscopy. The nature of the contents of a vacuole may…

Introduction The congenital myopathies are a clinically, genetically and pathologically heterogeneous group of muscle disorders defined in many patients by the presence of particular histopathological features. They emerged as a group of disorders with the wider application of histochemistry and electron microscopy in the 1950s and 1960s, when abnormal structural defects were identified in association with a particular phenotype, before any molecular causes were known. Historically,…

Facioscapulohumeral muscular dystrophy, myotonic muscular dystrophy and oculopharyngeal muscular dystrophy are dominantly inherited disorders, all of which have an unusual molecular defect involving nucleotide repeats. Clinically, facial weakness is a prominent characteristic of all of them. Facioscapulohumeral Muscular Dystrophy Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common muscular dystrophies, with an estimated prevalence of 1: 8300 to 1:15,000 and a high frequency of sporadic…

Joint contractures are a common complication of several neuromuscular disorders, but in some they are an early feature and specific joints are commonly affected. In particular, disorders known as Emery–Dreifuss muscular dystrophies are characterized by elbow contractures and often associated with a rigid spine and cardiac defects. In this chapter we focus on the Emery–Dreifuss syndromes, in particular those related to defects associated with proteins of…