Myopathy

DISEASES OF MUSCLE

myopathy is a muscle disease unrelated to any disorder of innervation or neuromuscular junction.
These conditions have widely varying etiologies, including congenital or inherited, idiopathic, infectious, metabolic, inflammatory, endocrine, and drug-induced or toxic.

CLINCIAL PICTURE

Proximal, large muscles.
Steadily progressive , s.t. episodic
Symmetric
Preserved tone and tendon reflexes
No sensory\autonomic abnormality
Cardiac failure
Cardiac conduction abnormalities
Respiratory problems (sleep apnea)

Outline of investigations

Creatine phosphokinase (CK)
EMG-NCS
Muscle Biopsy (histo-biochemistry)
ECG
CXR
Underlying cause:
Genetic\metabolic screen and counseling
Inflammatory/Endocrine/Electrolytes etc..


Hereditary myopathies
Muscular dystrophies
Metabolic myopathies
Mitochondrial myopathies
channelopathy

Acquired myopathies

inflammatory myopathies
Endocrinologic
Drugs and toxins

MUSCULAR DYSTROPHIES

This is a group of inherited disorders characterised by progressive degeneration of groups of muscles, sometimes with involvement of the heart muscle or conducting tissue, and other parts of the nervous system
Myotonic dystrophy (DM1).
Duchenne.
Becker.
Facioscapulohumeral (FSH).
Oculopharyngeal.
Emery-Dreifuss.

Clinical features

Onset is often in childhood, although some patients, especially those with myotonic dystrophy, may present as adults.
Wasting and weakness are usually symmetrical,
no fasciculation ,
no sensory loss,
tendon reflexes are preserved until a late stage, except in myotonic dystrophy.
Differential diagnosis is based on the age at onset, the distribution of affected muscles and the pattern of inheritance.
Many dystrophies include cardiomyopathy


Investigations
The diagnosis can be confirmed by specific molecular genetic testing, supplemented with EMG and muscle biopsy if necessary.
Creatine kinase is markedly elevated in Duchenne muscular dystrophy, but is normal or only moderately elevated in the other dystrophies.
Screening for an associated cardiac abnormality (cardiomyopathy or dysrhythmia) is important.

Myotonic dystrophy (DM1)

Autosomal dominant.
Affect any age.
Face (incl. ptosis), sternomastoids, distal limb, generalised later.
Myotonia, cognitive dulling, cardiac conduction abnormalities, lens opacities, frontal balding, hypogonadism.

Duchenne

X-linked; deletions in dystrophin gene.
First 5 years.
Proximal and limb girdle.
Pseudohypertrophy of calves.
Cardiomyopathy.

Other variants of dystrophinopathy

Becker muscular dystrophy :
Is a mild form of dystrophinopathy, Patient may live many decades with mild to moderate symptoms.
onset usually is after 12 years of age.
Progressive weakness of girdle muscles

type

Duchenne
Becker
Onset
Before 5 years
Early childhood to adult
Clinical Features

Progressive weakness of girdle muscles
Unable to walk after age 12

Progressive weakness of girdle muscles
Able to walk after age 15

Mental impairment

Common
uncommon


Facioscapulohumeral (FSH)
Autosomal dominant.
7-30 years.
Face and upper limb girdle.
Winging of scapula.

Emery-Dreifuss

4-5 years
Humero- peronal, proximal limb girdle later
Contractures develop early.
Cardiac involvement leads to sudden death

CHANNELOPATHIES

Inherited abnormalities of the sodium, calcium and chloride ion channels in striated muscle produce various syndromes of familial periodic paralysis, Myotonia and malignant hyperthermia

Hypokalaemic periodic paralysis

a muscle calcium or sodium channel disorder
autosomal dominant
Attacks are precipitated by a period of exercise followed by rest or by carbohydrate loading. Attacks typically develop in the early hours of the morning and may last hours to days.
Serum potassium is typically low at the onset but may normalize quickly.
patients with hypokalaemic paralysis will notice improvement with potassium ingestion but worsening with glucose.
Thyroid disorder mainly hyperthyroidism can associated with the disease.


Hyperkalaemic periodic paralysis
sodium channel
In hyperkalaemic periodic paralysis (hyperPP) patients typically experience recurrent attacks of muscle weakness
Precipitants include rest following exercise, cold, potassium ingestion or stress.
Attacks may vary in severity from mild weakness to total paralysis, The duration of attacks is usually less than 2 hours.
Many attacks are brief and do not require treatment.
If necessary, acute attacks can be terminated by ingestion of carbohydrate or inhaled salbutamol.
Preventative treatment with acetazolamide or a thiazide diuretic may be required.

Drug induced myopathy

Corticosteroids
Chloroquine
Amiodarone
β-blockers
Statins
Vincristine
Zidovudine
Opiates