Myopathy

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Myopathy

The myopathies are neuromuscular disorders in which the primary symptom is muscle weakness due to dysfunction of muscle fiber. Other symptoms of myopathy can include muscle cramps, stiffness, and spasm. Myopathies can be inherited or acquired. Myopathy means disease of muscle. Myopathy is a general term that refers to diseases that affect the muscles that connect to the bones.

Pathophysiology of myopathy:

The congenital myopathies are a diverse group of genetic skeletal muscle diseases, which typically present at birth or in early infancy. There are multiple modes of inheritance and degrees of severity.

Types of myopathy:

Ø Viral infections like HIV, Influenza, Epstein-Barr.

Ø Bacterial pyomyositis.

Ø Lyme disease.

Ø Parasitic infections like trichinosis, toxoplasmosis, cysticercosis.

Ø Fungal infections like candida, coccidiomycosis.

Classification of myopathies:

Hereditary:

Ø Congenital myopathies.

Ø Muscular dystrophies.

Ø Myotonia and channelopathies.

Ø Primary metabolic myopathies.

Ø Mitochondrial myopathies.

Acquired:

Ø Inflammatory myopathies– Polymyositis.

Ø Infectious myopathies.

Ø Endocrine myopathies.

Ø Secondary metabolic myopathies.

Ø Drug-induced and toxic myopathies.

Different types of myopathies:

Ø Muscular dystrophies: This type includes progressive weakness of the voluntary muscles and is sometimes evident at birth. Muscular dystrophies are characterized by progressive degeneration of muscle tissue due to abnormal or insufficient structural support proteins being present. They all involve the arms and/or legs to varying degrees, and some involve the muscles of the eyes or face.

§  Duchenne

§  Becker

§  Emery- Driefuss

§  Limb-girdle

§  Myotonic

§  Congenital.

Ø Toxic myopathy: Toxic myopathy happens when a toxin or medication interferes with muscle structure or function.                                                                                                     Toxins: Alcohol   and toluene.                                                                            Medications: Checkpoint inhibitor immunotherapy, corticosteroids (prednisone), Cholesterol – lowering drugs, amiodarone, colchicine, chloroquine, antivirals and protease inhibitors used in the treatment of HIV infection, omeprazole.

Ø Tetany: This features prolonged spams of the arms and legs.

Ø Congenital myopathy: This type of myopathy is evident by developmental delays in motor skills, as well as skeletal facial abnormalities often evident at birth. This type includes central core disease. Symptoms of congenital myopathies usually start at birth or in early childhood, but may not appear until the teen years or even later in adulthood.

§  Nemaline Myopathy:

v Diaphragm weakness

v Distal weakness in lower extremities

v Severe facial and bulbar weakness.

§  Centronuclear Myopathy:

v  Progressive ophthalmoparesis.

v Early respiratory failure in boys.

v Progressive craniofacial deformities.

§  Central core disease (Including minicore):

v Muscle pain/ cramps.

v MH.

v Dominant inheritance.

§  Fiber type disproportion:

v Low tone without other distinguishing characteristics.

Congenital myopathy	Onset	Prognosis
Centronuclear myopathy, X-linked (myotubular myopathy)	Prenatal-congenital	Death during infancy, some survive to adulthood
Centronuclear myopathy, classic	Late infancy-early childhood	Ambulation until adolescence
Centronuclear myopathy, adult	Infancy second to third decade	Slowly progressive
Nemaline myopathy, severe (neonatal)	Birth	Death in neonatal period
Nemaline myopathy, typical (classic)	First year	Many survive to adulthood
Nemaline myopathy, childhood	prepubertal	Many survive to adulthood
Nemaline myopathy, adult	Third to sixth decade	Adulthood
Central core, classical	Infancy	Adulthood?
Congenital fiber-type disproportion	First year	Variable
Multiminicore disease	Infancy – early childhood	Variable
Actin myopathy	Congenital	High mortality
Bethlem myopathy	First or second decade	Good
Desmin and desmin-related (Myofibrillar) myopathies	Second to fourth decade	Some patients lose ambulation

Ø Metabolic myopathy: Metabolic myopathies are myopathies that result from defects in biochemical metabolism that primarily affect muscle. Defects in genes that code for enzymes that are needed for normal muscle function and movement cause metabolic myopathies.

§  Acid maltase deficiency.

§  Carnitine deficiency.

     Symptoms:

Fatigue and exercise intolerance.

Muscle cramping.

Heart problems.

Difficulty breathing if the disease affects muscles involved in respiration.                                                    

Ø Mitochondrial myopathy: This type is caused by genetic abnormalities in the mitochondria, the structures in the cells that control energy. These conditions have muscle weakness, but also a variety of other symptoms, as mitochondrial disorders typically affect other organ systems like heart, brain and gastrointestinal tract.  This includes kearns – sayre syndrome, myoclonic epilepsy with ragged red fibers, and mitochondrial encephalomyopathy, lactic acidosis, and stroke like.

Ø Glycogen storage diseases of muscle: These are due to mutations in the genes controlling the enzymes that metabolize blood sugar. These include Pompe disease, Andersen disease, and cori disease. Myopathy of metabolic origin in childhood occurs due to a variety of conditions. Pompe’s disease also known as glycogen storage disease type II, is a rare storage disorder with clinical presentation akin to spinal muscular atrophy.

Ø Channelopathies: Channelopathies are diseases that develop because of defects in ion channels caused by either genetic or acquired factors. Mutations in genes encoding ion channels, which impair channel function, are the most common cause of channelopathies. Channelopathies are a group of cardiac conditions that display defects in ion channel and transporter function.                                                                                                     Types of channelopathies:

Ø Channelopathies that primarily affect neurons include certain types of epilepsy, ataxia, migraine, hyperekplexia, blindness, deafness, and peripheral pain syndromes.

Ø Myositis ossificans: In this condition, bone grows in muscle tissue.

Ø Myotonia congenita: Myotonia congenita is a disorder that affects muscles (skeletal muscles) used for movement. Beginning in childhood, people with this condition experience bouts of sustained muscle tensing that prevent muscles from relaxing normally.

Ø Neuromyotonia: This features alternating episodes of twitching and stiffness.

Ø Inflammatory myopathy

Ø Familial periodic paralysis: This features episodes of weakness in the arms and legs.

Ø Endocrine myopathy: Endocrinopathies, such as thyroid and parathyroid diseases, disorders of the adrenal axis, and acromegaly are included among the many causes of myopathy. Muscle disturbances caused by endocrine disorders are mainly due to alterations in the protein and carbohydrate metabolisms.                                                                                         Thyroid: Low thyroid is more common, but increased thyroid can also be problematic.                                                                                                         Parathyroid: Hyperparathyroidism resulting in increased calcium levels.       Adrenal: Addison’s disease and cushing syndrome.

Ø Stiff – person syndrome: This condition includes episodes of rigidity and reflex spasms.

Ø Electrolyte imbalance: High or low levels of the following electrolytes can interfere with muscle function:                                                                                            Potassium: Hypokalemia, hyperkalemia.                                                                                             Magnesium: Hypermagnesemia.

Causes of acquired myopathy:

Ø Infections: In some cases, it can be an infection that causes myopathy.

Ø Autoimmune reactions: Inflammatory myopathy occurs when the body starts to attack the muscle tissue and/or impedes muscle function. Autoimmune conditions such as sarcoidosis, lupus, and rheumatoid arthritis can all contribute to this type of myopathy.

Ø Alcohol: Alcohol abuse can cause myopathy as well as other health issues.

Ø Medical conditions: There are many medical conditions that can lead to myopathy.

Ø Nutritional deficiencies: A lack of certain vitamins and minerals can contribute to myopathy.

Ø Drug – induced myopathy: Certain types of drugs have been known to damage muscle fibers and can lead to what is known as drug – induced myopathy.

Symptoms of myopathy:

Ø Muscle weakness (main symptom of myopathy), most commonly of your upper arms and shoulders and thighs.

Ø Tripping or falling.

Ø Muscle cramps, stiffness and spasms.

Ø Difficulty swallowing or breathing.

Ø Fatigue with exertion.

Ø Lack of energy.

Ø Muscle soreness.

Ø Muscle wasting around the shoulders and hips.

Diagnosis:

Blood tests:

Ø Muscle enzymes such as creatine kinase or aldolase may be elevated in certain myopathies as a result of the breakdown of muscle fibers.

Ø Electrolyte levels such as sodium, magnesium, potassium, calcium and phosphorus.

Ø Autoimmune disease testing such as antinuclear antibodies, rheumatoid factor, sedimentation rate and c-reactive protein.

Ø Endocrine testing such as thyroid hormone.

Electromyography

Magnetic resonance imaging – of the muscles.

Genetic tests

Muscle biopsy.

 Physiotherapy treatment for myopathies:

Ø Neurological physiotherapists can help control the symptoms, such as muscular weakness and spasms, and enable you to maintain a good quality of life.

Ø Treatment usually includes stretching and strengthen exercises to help maintain muscle strength and flexibility.

The benefits of physiotherapy are:

Ø Increased muscle strength

Ø Increased balance

Ø Increased flexibility

Ø Reduced risk of falls.

Ø Stop the development of muscular and joint contractures

Ø Provide equipment for mobility if required ie. Walking aids, orthoses, calipers and wheelchairs

Ø Advise on moving and handling techniques and equipment

Ø Refer to other appropriate medical health professionals, with the consent

Ø Anticipate and minimize other secondary complications of myopathies.