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Myotonic Muscular Dystrophy

In this not only striated muscle severely affected but smooth muscle of the alimentary tract and uterus is also involved, cardiac function is altered and patient have multiple and variable endocrinopathies, immunologic deficiencies, cataracts, dysmorphic facies, intellectual impairment.


Other characteristic features:

  1. Myotonia
  2. Distal distribution of muscle weakness and wasting myalgia do not occur
  3. Exhibits a pattern of anticipationQ in which each successive generation has a tendency to be more severely involved than previous generation. 

VII. Spinal Muscular Atrophies



A. ​Spinal Muscular Atrophies


Spinal Muscular Atrophies (SMA) are degenerative disease of motor neurons that begin in fetal life and continue to be progressive in Infancy and childhood.

Three Types

  1. Severe infantile form Werdnig Hoffmann disease Type-I
  2. Late Infantile form Type-II
  3. Chronic or juvenile form Kugelberg – Welander disease Type-III 

Clinical Manifestations


Type – 1

  1. Loss of fetal movement in later part of pregnancy and polyhydroamniosQ
  2. Severe hypotoniaQ
    Generalized weakness
    Thin muscle mass
    DTR absentQ
    Involvement of tongue, face and jaw muscle and sparing of extra ocular muscle and sphinctersQ
  3. Having respiratory distress and unable to feed. Death occurs with in 2 year. 

Type – 3 Kagelberg Welander disease

  1. May appear normal in infancy
  2. The progressive weakness is proximal in distribution
  3. Fasciculation are specific clinical sign of denervation of muscle. Q
  4. Myalgia are not a feature of SMAQ
  5. Heart is not involved and intelligence is normalQ 

Table: Inflammatory myopathies


  1. Juvenile dermatomyositis
  2. Polymyositis
  3. Inclusion body myositis
  4. Myositis as overlap syndrome
  5. Others:
    1. eosinophilic myositis
    2. Focal nodular myositis
    3. Sarcoid myopathy


  1. Viral myositis:
    1. Influenza
    2. human immunodeficiency virus
    3. others
  2. Parasitic myositis
    1. trichinosis
    2. toxoplasmosis
    3. cysticercosis
  3. Bacterial myositis
  4. Fungal myositis 

Table: Causes of floppy infant syndrome

Central nervous system


Perinatal asphyxia, neonatal encephalopathy, kernicterus, cerebral palsy (atonic type), intracranial hemorrhage, chromosomal anomalies including Down syndrome, inborn errors of metabolism (aminoaciduria, mucopolysaccharidosis, cerebral lipidosis)

Spinal cord


Anterior horn cell disease: Werdnig Hoffman (spinal muscular atrophy), poliomyelitis

Peripheral nerves


Familial dysautonomia, hereditary motor sensory neuropathy

Myoneural junction


Neonatal myasthenia gravis, infantile botulism, following antibiotic therapy



Muscular dystrophies, congenital myotonic dystrophies, congenital myopathies (central core disease, nemaline myopathy), polymyositis, glycogen storage disease, arthrogryphosis multiplex congenita



Protein energy malnutrition, hypothyroidism, rickets, Prader¬Willi syndrome, Ehler-Danlos syndrome, cutis laxa


Differentiating features of a floppy infant according to site of involvement


Extent of weakness





Site of involvement




Proximal vs distal weakness

Deep tendon reflexes


Muscle biopsy






Normal or increased



Anterior horn cell






Denervation potentials, Fasciculations

Neurogenic atrophy

Peripheral nerve





Decreased / absent

Abnormal NCS, Denervation potentials

Denervation pattern

Neuromuscular junction






Decremental response on repetitive stimulation








Short duration, polyphasic potentials


EMG electromyography; NCS nerve conduction studies

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