Bone disease

What are the main classifications of skeletal muscle diseases?

Muscular dystrophies, mitochondrial myopathies, metabolic myopathies, inflammatory myopathies, toxic/drug-induced myopathies, endocrine-related myopathies, and myopathies of miscellaneous etiology.

What is a key feature of muscular dystrophies?

Inherited progressive muscle disorders characterized by muscle fiber degeneration and weakness.

What is Duchenne Muscular Dystrophy (DMD)?

An X-linked recessive disorder caused by a mutation in the dystrophin gene, leading to total absence of dystrophin.

What is the incidence rate of Duchenne Muscular Dystrophy (DMD)?

1 in 3,500 live male births.

What clinical feature is associated with Gower's sign in DMD?

The use of hands and arms to 'walk up' the legs to stand from a squatting position.

What is the prognosis for individuals with Duchenne Muscular Dystrophy?

Most patients die before the age of 20-30 years, usually due to respiratory failure.

How is dystrophin relevant to muscular dystrophies?

Dystrophin is a crucial protein that links the cytoskeleton of muscle fibers to the basement membrane; its absence leads to muscle cell damage and weakness.

What are the clinical features of Becker Muscular Dystrophy (BMD)?

Later onset and slower progression of muscle weakness, pseudohypertrophy of calves, waddling gait, and heart problems.

How does the dystrophin in Becker Muscular Dystrophy differ from DMD?

In BMD, dystrophin is reduced but present, whereas in DMD, it is absent.

What characteristic pathology is observed in DMD muscle biopsy?

Diffuse variation in fiber size, increased adipose tissue, and loss of dystrophin.

What are mitochondrial myopathies?

Disorders caused by mutations in mitochondrial or nuclear DNA that affect mitochondrial function.

What are common clinical features of mitochondrial myopathies?

Muscle weakness, fatigue, exercise intolerance, lactic acidosis, and heart problems.

What does MELAS stand for in mitochondrial myopathies?

Mitochondrial Encephalopathy, Lactic Acidosis, Stroke-like episodes.

What is a significant complication of dermatomyositis?

Interstitial lung disease (ILD) and increased risk of certain cancers.

What skin features are characteristic of dermatomyositis?

Heliotrope rash and Gottron’s papules.

What distinguishes polymyositis from other forms of myopathy?

It is an acquired autoimmune disorder characterized by muscle inflammation and weakness.

What is a common diagnostic test for determining polymyositis?

Muscle biopsy showing variation in muscle fiber size and endomysial inflammation.

What are the major features of inclusion body myositis?

Slowly progressive weakness, particularly in distal muscles, dysphagia, and muscle atrophy.

What is the typical age distribution for inclusion body myositis?

Typically affects adults over the age of 50.

What are the two main types of myopathies of miscellaneous etiology?

Statin-induced myopathy and steroid myopathy.

What is the main cause of hypothyroid myopathy?

Underactive thyroid gland leading to muscle weakness and metabolic impairment.

How can hyperthyroid myopathy affect muscle?

It causes muscle weakness and atrophy due to increased muscle protein breakdown.

What are common laboratory findings in polymyositis?

Elevated creatine kinase (CK) and aldolase levels.

What results might indicate mitochondrial myopathy during muscle biopsy?

Ragged red fibers on Gomori trichrome stain.

What are common symptoms of metabolic myopathies?

Exercise intolerance, muscle cramps, weakness, and fatigue.

How does McArdle disease manifest?

Exercise intolerance triggered by activity, muscle cramps, and myoglobinuria.

What symptoms are associated with Pompe disease?

Severe muscle weakness, heart failure, and macroglossia in infants.

What is the incidence of dermatomyositis in the population?

Around 1 in 100,000 individuals.

What role do autoantibodies play in dermatomyositis?

Contribute to muscle damage through both humoral and cellular immunity.

What is a common outcome for statin-induced myopathy?

Muscle pain, weakness, and elevated CK levels.

What characterizes toxic myopathies?

Muscle damage resulting from substances, including drugs and toxins.

What other endocrine disorders can lead to muscle weakness?

Cushing's syndrome, acromegaly, and diabetes mellitus.

What is the role of corticosteroids in muscle health?

While they can promote muscle atrophy with long-term use, anabolic steroids lead to muscle hypertrophy.