Myopathies and Their Etiology

Study Notes

Myopathies are gradual, progressive, degenerative disorders affecting muscles.
Muscular dystrophies are a genetically determined type of myopathy, featuring a gradual, progressive degeneration of muscles.

Symptoms:
- Clumsy gait
- Inability to climb stairs
- Protuberant abdomen
- Weakness and wasting of specific muscle groups (selectivity)
Signs:
- Weakness of skeletal muscles, specifically proximal muscles are affected more severely than distal muscles
- Loss of muscle tone (hypotonia), diminished reflexes (hyporeflexia) in lower motor neuron type
- Bilateral and symmetrical muscle involvement
- Winging of scapulae, pot-belly abdomen, exaggerated lumbar lordosis, waddling gait, and positive Gower's sign (indicates proximal muscle weakness) can be associated with specific types of myopathies
Selectivity: In some dystrophies, specific muscle parts, like the sternal head of pectoralis major, are weaker than the clavicular head.
Facial muscles: Can be affected bilaterally in some types of myopathies
Pseudohypertrophy: Enlargement of certain muscles in some types, like quadriceps and gastrocnemius muscles in lower limbs, and deltoid, supraspinatus, and infraspinatus muscles in upper limbs
Contractures: Can lead to bone deformities
ECG changes: May be seen in specific types, like Duchenne muscular dystrophy
No sensory or sphincter issues: No signs of nerve damage or issues with bladder or bowel control

Laboratory investigation: Serum creatine phosphokinase (CPK) levels are usually elevated in some myopathy types. Urinary creatine levels are also sometimes investigated
Neurophysiology: Electromyography (EMG) often shows low amplitudes and durations of motor unit potentials, and early interference patterns.
Other: Muscle biopsies (especially in dystrophinopathies) and MRI scans may also be utilized

Various types exist, categorized as shoulder girdle, limb girdle, and pelvic girdle muscular dystrophies.
Specific types include:
- Fascioscapulohumoral myopathy (AD)
- Limb girdle muscular dystrophies (AR)
- Pseudo-hypertrophic muscular dystrophy (Duchenne's and Becker's MD – X-linked recessive)
- Atrophic type (AR)

Physiotherapy
Orthopedic surgery: Tenotomy for contractures
Care of the bedridden
Genetic counseling: To identify carriers, especially significant in familial conditions

Definition: Acquired autoimmune inflammatory disease of skeletal muscles
Etiology:
- Systemic infection
- Collagen disease
- Immunization
- Paraneoplastic conditions (related to cancer)
Clinical picture:
- Acute or subacute onset with general symptoms like fatigue
- Pain and tenderness over muscles
- Weakness affecting proximal muscles of upper limbs (UL) and lower limbs (LL) , including posterior neck muscles and pharyngeal and laryngeal muscles
- Deep reflexes remain intact
- Skin manifestations may exist in dermatomyositis
Investigations:
- Raised erythrocyte sedimentation rate (ESR)
- Raised serum CPK levels
- Electromyography (EMG) showing myopathic patterns with fibrillations
- Detection of circulating antibodies (like antinuclear antibodies, rheumatoid factor)
Treatment:
- Prednisolone (60mg daily)
- Other immunosuppressive drugs
- Addressing the underlying cause (if any) is also crucial

Definition: Episodes of transient paralysis from alterations in serum potassium levels
- Hypokalaemic periodic paralysis is triggered by high carbohydrate intake, and rest after exercise, usually occurring upon waking in the morning
- Hyperkalemic periodic paralysis is triggered by cold exposure or intensive exercise immediately after exercise
Symptoms:
- Weakness in muscles, initially in lower limbs, then upper limbs developing into quadriplegia
- Myotonia (muscle stiffness)
Duration and intensity of paralysis: Generally hours to days in Hypokalaemic, and less then an hour in hyperkalemic types
Serum potassium levels: Reduced in hypokalaemic and increased in hyperkalemic types
Treatment:
- Intravenous potassium chloride (KCl) for hypokalaemia
- Calcium gluconate infusion, and oral prophylactic acetazolmide, plus glucose and insulin infusions for hyperkalemia
- Thiazide diuretics in hyperkalemia