Dystrophia Myotonica - Clinicals, Diagnosis, and Management

Neurology

Clinicals - History

Fact Explanation
Difficulty in relaxing hand grasp Slow relaxation of muscles after contraction. Difficulty in relaxing hand grasp
Slow relaxation of muscles after contraction.
Visual impairment Development of cataract due to same genetic defect as that causing muscle atrophy and myotonia. Visual impairment
Development of cataract due to same genetic defect as that causing muscle atrophy and myotonia.
Difficulty in swallowing Weakness of muscles in pharynx. Difficulty in swallowing
Weakness of muscles in pharynx.
Loss of weight Due to muscle wasting. Loss of weight
Due to muscle wasting.
Impotence Due to hypogonadism with low testosterone levels. Impotence
Due to hypogonadism with low testosterone levels.
Baldness Same genetic defect on chromosome 19 causes baldness. Baldness
Same genetic defect on chromosome 19 causes baldness.
Weakness in limbs Due to muscle wasting. Weakness in limbs
Due to muscle wasting.
Sudden falling like a log while walking Myotonia causing sudden inability to maintain balance. Sudden falling like a log while walking
Myotonia causing sudden inability to maintain balance.

Clinicals - Examination

Fact Explanation
Tapping the thenar eminence of hand causes a dimple which persists for a while Failure of immediate muscle relaxation after contraction has ceased. Tapping the thenar eminence of hand causes a dimple which persists for a while
Failure of immediate muscle relaxation after contraction has ceased.
Ptosis Weakness of levator palpebrae superioris muscle. Ptosis
Weakness of levator palpebrae superioris muscle.
Atrophy of testicles Primary gonadal failure with high serum FSH and LH hormone levels and low testosterone levels. Atrophy of testicles
Primary gonadal failure with high serum FSH and LH hormone levels and low testosterone levels.
Atrophy of face and neck muscles Muscle atrophy due to triplet expansion in chromosome 19. Atrophy of face and neck muscles
Muscle atrophy due to triplet expansion in chromosome 19.
Tapping the lateral border of tongue causes a deep dimple at the site of impact which persists for a while Due to persistent muscle contraction without immediate relaxation . Tapping the lateral border of tongue causes a deep dimple at the site of impact which persists for a while
Due to persistent muscle contraction without immediate relaxation .
Tachycardia or bradycardia or irregular pulse Due to fibrosis and fatty infiltration of conducting system and AV node. Tachycardia or bradycardia or irregular pulse
Due to fibrosis and fatty infiltration of conducting system and AV node.

Investigations - Diagnosis

Fact Explanation
Electromyography This shows a combination of myotonic discharges and myopathic appearing motor units. Characteristic bursts of repetitive potentials which vary both in potential and frequency are called "dive bomber" potentials. Electromyography
This shows a combination of myotonic discharges and myopathic appearing motor units. Characteristic bursts of repetitive potentials which vary both in potential and frequency are called "dive bomber" potentials.
Serum creatinine level May be mildly elevated. Serum creatinine level
May be mildly elevated.
Muscle biopsy This is histologically grossly abnormal in clinically affected patients. Features include fibrosis, variability in fiber size, sarcoplasmic masses etc. Muscle biopsy
This is histologically grossly abnormal in clinically affected patients. Features include fibrosis, variability in fiber size, sarcoplasmic masses etc.
Genetic testing (Polymerase chain reaction and southern blotting) This is the mainstay of diagnosis. It shows the CTG trinucleotide repeat expansion in gene which codes for a myosine kinase expressed in skeletal muscle. Genetic testing (Polymerase chain reaction and southern blotting)
This is the mainstay of diagnosis. It shows the CTG trinucleotide repeat expansion in gene which codes for a myosine kinase expressed in skeletal muscle.

Investigations - Management

Fact Explanation
ECG Should be done yearly to detect cardiac arrhythmia. ECG
Should be done yearly to detect cardiac arrhythmia.
Sleep study For any symptoms of excessive daytime sleepiness and obstructive sleep apnoea. Sleep study
For any symptoms of excessive daytime sleepiness and obstructive sleep apnoea.
Fasting blood sugar There is no significant increase in incidence of diabetes mellitus among patients with Dystrophia Myotonica compared to the general population. However there is evidence of insulin resistance due to abnormal splicing of the insulin receptor
mRNA to a more insulin insensitive isoform. Therefore any clinical suspicion of diabetes mellitus should prompt a fasting blood sugar test.
Fasting blood sugar
There is no significant increase in incidence of diabetes mellitus among patients with Dystrophia Myotonica compared to the general population. However there is evidence of insulin resistance due to abnormal splicing of the insulin receptor
mRNA to a more insulin insensitive isoform. Therefore any clinical suspicion of diabetes mellitus should prompt a fasting blood sugar test.
Prenatal molecular diagnosis This can be done using retrieved transcervical trophoblastic cells or maternal plasma. Prenatal molecular diagnosis
This can be done using retrieved transcervical trophoblastic cells or maternal plasma.

Management - Supportive

Fact Explanation
Dehydroepiandrosterone (DHEA) Initial pilot studies suggested improvement of muscle power. But a recent multicentre, randomised, double-blind. placebo controlled study did not substantiate this. Dehydroepiandrosterone (DHEA)
Initial pilot studies suggested improvement of muscle power. But a recent multicentre, randomised, double-blind. placebo controlled study did not substantiate this.
Exercise training This can maximize muscle and cardio respiratory function and prevent disuse atrophy of muscles. Exercise training
This can maximize muscle and cardio respiratory function and prevent disuse atrophy of muscles.
Sodium channel blockers Myotonia is the main cause of disability in patients with dystrophia myotonica.Myotonia could be caused by inactivation defect of Sodium channels causing long-lasting depolarisation of the muscle fiber. Thus blocking these channels can relieve myotonia. Sodium channel blockers
Myotonia is the main cause of disability in patients with dystrophia myotonica.Myotonia could be caused by inactivation defect of Sodium channels causing long-lasting depolarisation of the muscle fiber. Thus blocking these channels can relieve myotonia.
Benzodiazepines: Diazepam Probably due to membrane stabilizing effect. Benzodiazepines: Diazepam
Probably due to membrane stabilizing effect.
Calcium antagonists: Nifedipine High concentrations of Calcium have been found in red blood cells and skeletal muscle in myotonic dystrophy. Thus by blocking calcium channels myotonia gets relieved. Calcium antagonists: Nifedipine
High concentrations of Calcium have been found in red blood cells and skeletal muscle in myotonic dystrophy. Thus by blocking calcium channels myotonia gets relieved.
CNS stimulant drugs Modafinil 200-400 mg/day - The mechanism of action of modafinil is still not completely understood, but it is associated with an activation of the tuberomamillary nucleus and orexin-containing neurons.
Methylphenidate and Dexamphetamine:
these drugs are useful in the sleep disordered. breathing.
CNS stimulant drugs
Modafinil 200-400 mg/day - The mechanism of action of modafinil is still not completely understood, but it is associated with an activation of the tuberomamillary nucleus and orexin-containing neurons.
Methylphenidate and Dexamphetamine:
these drugs are useful in the sleep disordered. breathing.
Dietary manipulation Thickening food, adding supplements and adopting safer swallowing techniques help to overcome dysphagia. Dietary manipulation
Thickening food, adding supplements and adopting safer swallowing techniques help to overcome dysphagia.
Tricyclic anti depressive drugs: Imipramine, Clomipramine It has been hypothesized that myotonic dystrophy is caused by a generalized disorder of membrane aminergic and petidergic receptors. Thus Inhibition of re uptake of neurotransmitters can benefit myotonia. Tricyclic anti depressive drugs: Imipramine, Clomipramine
It has been hypothesized that myotonic dystrophy is caused by a generalized disorder of membrane aminergic and petidergic receptors. Thus Inhibition of re uptake of neurotransmitters can benefit myotonia.

Management - Specific

Fact Explanation
Gene therapy This is the only mode of definitive treatment. However this option is still at in vitro experimental level. Gene therapy
This is the only mode of definitive treatment. However this option is still at in vitro experimental level.

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