Muscle Disorders and Myopathies Quiz

Myopathy: Definition and General Classifications

• Myopathy is a general term for muscle disease not related to nerve or neuromuscular junction disorders.
• It encompasses a wide range of etiologies.
• Myopathy typically leads to muscle weakness and atrophy, particularly affecting proximal muscles like those in the thighs and shoulders.

Hereditary Myopathies (Primary)

• Hereditary myopathies are inherited conditions primarily impacting skeletal muscle tissue.
• These disorders result from mutations in genes encoding proteins crucial for muscle structure and function.

Muscular Dystrophies (Primary)

• Muscular dystrophies are a heterogeneous group of inherited diseases affecting both children and adults.
• At least 30 different genes contribute to the development of these illnesses.
• Duchenne and Becker muscular dystrophies are common forms.
• These diseases result from genetic defects on the X chromosome.
• They are characterized by muscle wasting (atrophy), weakness, and elevated creatine phosphokinase (CPK) levels.

Congenital Myopathies (Present at Birth)

• Congenital myopathies are characterized by the absence of necrotic or degenerative changes within muscles.
• Contrasting muscular dystrophies, CPK levels in these conditions are often normal.
• Well-established conditions within this group include nemaline myopathy, central core disease, X-linked myotubular myopathy, and centronuclear myopathy.

Metabolic Myopathies

• Metabolic myopathies comprise a diverse range of disorders stemming from defects in cellular energy metabolism.
• These defects affect the breakdown of fatty acids and carbohydrates, hindering the generation of adenosine triphosphate (ATP).

Mitochondrial Myopathies

• Mitochondrial myopathies are a large group of disorders arising from primary dysfunction in the mitochondrial respiratory chain.
• This dysfunction often leads to muscle disease, and these conditions frequently involve multi-system dysfunction, along with genetic etiologies.

Genetic Defects

• Genetic defects affecting calcium, sodium, potassium, and chloride channels within skeletal muscles can lead to periodic paralyses and nondystrophic myotonias.
• Myotonia congenita, paramyotonia congenita, hyperkalemic periodic paralysis, and hypokalemic periodic paralysis, and potassium-aggravated myotonia are conditions resulting from such defects.

Acquired/Secondary Myopathies

• These types of myopathies develop later in life, as opposed to hereditary conditions.

Idiopathic Inflammatory Myopathies

• Polymyositis (PM) and dermatomyositis (DM) are examples of idiopathic inflammatory myopathies, characterized by muscle aches, tenderness, and weakness, often fluctuating over time.
• Patients may experience fever and appetite loss.
• DM is distinguished by a distinctive skin rash, typically a purple discoloration around the eyes and cheeks.

Endocrinologic Myopathies

• Steroid myopathy is the most common endocrine muscle disease, and is often linked to steroid excess.
• Cushing's syndrome (due to hormonal overproduction by the pituitary and adrenal glands) results in myopathy. Myopathies can also arise from excess parathyroid hormone resulting in hypercalcemia, a contributing factor to proximal muscle pain and weakness.
• Conditions such as hyperthyroidism, where thyroid glands produce excessive thyroxine, or hypothyroidism, from insufficient thyroxine production, can also cause myopathies, with muscle weakness being a symptom in both situations.

Toxic Myopathies

• Toxic myopathies result from exposure to certain medications/chemicals, including lipid-lowering agents, anesthetics, narcotics (e.g., cocaine, heroin, meperidine), corticosteroids, and excessive alcohol intake.
• These substances can harm skeletal muscle.

Diagnostic Investigations

• Diagnostic investigations for myopathies often involve a combination of:
  • Positive family history and genetic testing
  • Urine analysis
  • Elevated serum enzymes (like creatine kinase)
  • Nerve conduction studies
  • Electromyography (EMG)
  • Muscle biopsy
  • Protein analysis
  • DNA analysis

Clinical Classifications (of progressive muscular dystrophies)

• Shoulder girdle type, scapulo-humeral type, facio-scapulo-humeral type, pelvic girdle type, pseudo-hypertrophy type (duchenne, backer), LGMD Atrophic type, distal type of gower, ocular type, and oculo-pharyngeal type, and myotonic dystrophy are examples of clinically identified progressive types

Myasthenia Gravis

• Myasthenia gravis is a neuromuscular disorder characterized by muscle weakness, particularly affecting those controlled voluntarily.
• This weakness is accompanied by rapid muscle fatigue.
• It results from a breakdown in the normal communication between nerves and muscles.
• The disease is more common in women under 40 and men over 60.
• Symptoms generally worsen over time.

Myasthenia Gravis: Pathogenesis

• The immune system produces antibodies that block or destroy acetylcholine receptor sites on muscles.
• This blockage reduces stimulation of muscles, leading to weakness.
• Antibodies may also affect receptor tyrosine kinase function, which further contributes to impaired neuromuscular signaling, leading to weakness and fatigue of affected muscles.

Myasthenia Gravis: Symptoms

• Initial signs often include weakness of eye muscles.
• Conditions such as ptosis (drooping eyelids), diplopia (double vision), facial weakness, swallowing difficulties, and respiratory distress are possible symptoms.

Myasthenia Gravis: Assessment

• Assessing myasthenia gravis typically involves checking reflexes, evaluating muscle tone, testing eye movements while looking for muscle tone involvement, and applying repetitive nerve stimulation testing while checking for antibodies linked to MG. A CT scan or MRI of the chest is used to rule out tumors in affected regions.

Myasthenia Gravis: Treatment

• Medications, including immunosuppressants and corticosteroids, can help relieve symptoms and slow the progression of myasthenia gravis.
• Thymus gland removal might be helpful for certain patients with myasthenia gravis.
• Techniques like plasmapheresis (plasma exchange) and intravenous immunoglobulin (IVIG) therapy can also be used to manage symptoms.

Myasthenia Gravis: Complications

• Myasthenic crisis, a life-threatening complication involving severe muscle weakness, and respiratory distress.
• Individuals with myasthenia gravis have a higher likelihood of developing other autoimmune disorders, such as lupus or rheumatoid arthritis.

Myasthenia Gravis: Long-Term Outlook

• Long-term outcomes vary with myasthenia gravis; Some experience mild symptoms, while others require wheelchair assistance.
• Prompt diagnosis and appropriate treatment can usually help prevent disease progression.

Physical Therapy Examination

• Respiratory and motor assessments, including observations, palpation, individual or group muscle testing, muscle tone assessment, deep tendon reflex examination, range-of-motion examination and sensory assessments, are crucial for diagnosing myopathies and muscular dystrophies.

Physical Therapy Treatment for Myopathies

• Treatment involves a variety of approaches tailored to different stages of the diseases, including:
  • Muscle shortening exercises
  • Exercise programs
  • Heat applications
  • Technical applications (e.g., night splints)
  • Assistance with activities of daily living (ADL)
  • Parent instruction/education.
  • Equipment adjustments and adaptations

Treatment Prevention

• Prevention strategies focus on maintaining independent walking, ambulation, and preventing the need for wheelchair use based on the disease presentation.

Rehnold's Program for Muscular Dystrophies

• This program offers treatment strategies in various stages (walking, ambulant, and wheelchair dependent).
• Treatment methods include active exercises, passive range-of-motion, and breathing exercises, adapted to each stage.