Muscular Dystrophy Diagnosis and Treatment

Muscular Dystrophy

• Lack of dystrophin in muscle fibers
• EMG study:
  • Increased polyphasic action potential
  • Short duration of action potential
  • Decreased amplitude of mean action potential
• Treatment:
  • No specific drug treatment
  • Supportive treatment:
    • Vitamin E
    • Physiotherapy to delay weakness and contractures
    • Wearing light spinal supports and specific shoes
    • Ventilatory support in late terminal stages
    • Psychological support
  • Infrequent course of methyl prednisolone (1mg/kg/day) for transient improvement of power
  • Dealing with complications (e.g., bed sores, pneumonia)
  • Genetic counseling before marriage

Myasthenia Gravis (MG)

• Definition: Chronic disease due to disorder of transmission at the myoneural junction
• Etiology: Production of autoantibodies against acetylcholine (Ach) receptors by thymus gland
• Clinical features:
  • Muscular fatigability, may be restricted to a group of muscles
  • Descending march course
  • Tendency to relapse and remission
  • Permanent weakness in later stages
• Diagnosis:
  • Clinical diagnosis
  • Therapeutic test: 2mg of Tensilon (anticholine esterase) injected IV
  • Detection of serum anti-Ach receptor antibodies
  • X-ray chest, CT chest to detect thymoma
  • EMG study: decreased amplitude and decrementing response in CMAP

Myotonic Muscles Disorders

• Definition: Primary muscle disease characterized by myotonic phenomena (delayed relaxation of skeletal muscle after contraction)
• Clinical features:
  • Slowness in relaxation of hand grip
  • Persisting dimpling after sharp blow on a muscle belly
• Hereditary syndromes of myotonia:
  • Myotonia congenita: Early age of onset, generalized myotonia, painless stiffness of muscles, feeding difficulty, strangled cry
  • Myotonia dystrophica: Late age of onset, distal muscular dystrophy, trophic changes (e.g., cataract, frontal baldness, poor vision)

Inflammatory Muscles Diseases (Myositis)

• Acquired or idiopathic
• Clinically: muscle pain, tenderness, weakness, wasting
• Histopathologically: muscle fiber necrosis, regeneration, and interstitial inflammatory cell infiltration
• Types and causes:
  • Infective agents (e.g., viral, bacterial, parasitic myositis)
  • Connective tissue disease (e.g., rheumatoid arthritis, SLE)
  • Idiopathic polymyositis and dermatomyositis: autoimmune, common in females, adult life