Myotonic Dystrophy

Physical Examination

• Myotonia:

  • Grip Myotonia: Difficulty in releasing the hand after a firm grip.

  • Perioral Myotonia: Prolonged contraction and slow relaxation of muscles around the mouth.

  • Percussion Myotonia: Sustained muscle contraction induced by tapping on a muscle belly, such as the thenar eminence.

• Muscle Weakness:

  • Preferentially affects distal more than proximal muscles.

  • Notable in hands, feet, neck flexors, and facial muscles.

  • Muscle Wasting:

  • Visible in the temporalis, sternocleidomastoid, and distal limb muscles, often presenting a thin, wasted appearance.

• Facial Muscle Involvement:

  • Bilateral ptosis.

  • Facial muscle weakness leading to a "hatchet face" appearance and diminished facial expressions (mask-like facies).

• Gait Abnormalities:

  • A waddling gait may be evident due to hip muscle weakness.

  • Foot Drop: Weakness of the dorsiflexors of the foot, leading to challenges in foot clearance during walking.

• Absence of Deep Tendon Reflexes:

  • Reflexes such as the bicep, tricep, and ankle jerk may be reduced or absent.

• No Sensory Deficits:

  • Sensation generally remains intact, as myotonic dystrophy primarily affects the muscular system.

Additional Examination

• Cardiac Examination:

  • Palpation and Auscultation: Check for irregular pulse and murmurs.

• Respiratory Examination:

  • Inspection and Palpation: Look for use of accessory muscles indicating respiratory muscle weakness.

• Auscultation: Listen for reduced breath sounds that could reflect respiratory compromise.

• Endocrine Examination:

  • Thyroid Gland: Palpate the thyroid for enlargement or nodularity.

• Skin and Hair: Inspect for signs of endocrine dysfunction such as thin, dry skin, and frontal balding.

• Finger tips: Finger prick marks

Investigations

• Laboratory Tests

  • Creatine Kinase (CK): Often mildly elevated or normal, indicating some degree of muscle damage.

  • Serum Electrophoresis: To rule out other myopathies and systemic conditions.

  • Glucose and HbA1c Levels: Important for screening diabetes mellitus, which can be associated with myotonic dystrophy.

  • Thyroid Function Tests: To check for thyroid dysfunction, as endocrine issues are common in systemic diseases like myotonic dystrophy.

  • Imaging Studies

  • In postpubertal males, serum testosterone and FSH
    

• Imaging

  • Muscle Ultrasound or MRI: These imaging modalities are useful for assessing the extent of muscle wasting and fatty replacement of muscle tissue, which are characteristic findings in myotonic dystrophy.

  • MRI Brain: Helps in detecting any cerebral atrophy or white matter changes that might be associated with the cognitive aspects of myotonic dystrophy.

  • Echocardiogram: Essential for evaluating cardiac anatomy and function, given the risk of cardiomyopathy and cardiac conduction defects in myotonic dystrophy patients.

• Invasive Tests

  • Electromyography (EMG): Shows characteristic myotonic discharges with a "dive bomber" sound, essential for confirming the diagnosis. These discharges are sharp, repetitive spikes that occur when the muscle is stimulated, reflecting the pathological inability of muscles to relax promptly.

  • Muscle Biopsy: Although less commonly required now with genetic testing, can confirm diagnosis by showing dystrophic changes, increased internal nuclei, and ring fibers.

• Genetic Testing: Definitive diagnostic test, identifying the CTG trinucleotide repeat expansion in the DMPK gene.

• Other Tests

  • Electrocardiogram (ECG): To identify arrhythmias and conduction defects, frequent cardiac manifestations in myotonic dystrophy.

  • Pulmonary Function Tests: To assess respiratory capacity and function, especially because myotonic dystrophy can affect respiratory muscles, potentially leading to respiratory failure.

  • Ophthalmological Examination: Regular checks are recommended to monitor for the development of early-onset cataracts, another frequent complication.

Management

• General Management:

• Multidisciplinary team approach: Involving neurologists, cardiologists, respiratory therapists, endocrinologists, and genetic counselors.

• Patient and family education: Information on the genetic nature of the disease, potential complications, and inheritance patterns.

• Lifestyle adjustments: Encourage regular physical activity as tolerated and dietary modifications to manage weight and overall health.

• Medical Management:

• Symptomatic treatment of myotonia: Use of anti-myotonic drugs like mexiletine or phenytoin to reduce muscle stiffness.

• Management of cardiac issues: Regular monitoring with ECGs and echocardiograms, with the use of anti-arrhythmic drugs or pacemakers as indicated.

• Respiratory support: Use of non-invasive ventilation for patients with respiratory muscle weakness, especially at night.

• Endocrine disorders: Treatment of associated diabetes and thyroid dysfunction with medications as required.

• Pain management: Use of analgesics to manage musculoskeletal pain, a common complaint.

• Surgical Management:

• Cataract surgery: Early intervention for vision impairment due to cataract development.

• Orthopedic interventions: Surgery for foot drop or other musculoskeletal abnormalities that interfere with mobility.

• Pacemaker or implantable cardioverter-defibrillator (ICD) placement: For severe cardiac conduction defects.

• Other:

  • Genetic counseling: Crucial for patients and families to understand risks for offspring and other family members.

  • Psychosocial support: Access to psychological support and counseling to cope with chronic illness and its implications.

  • Regular monitoring and preventive care: Annual assessments or as needed to monitor progression and manage complications proactively.