Myotonic Dystrophy, Congenital Type
Background Histopathology & Immunohistochemistry Differential Diagnosis Myotonic Dystrophy, Adult Type
BACKGROUND AND CLINICAL INFORMATION:
Head
Summary:
Symptoms usually starts at birth and is
characterized by neonatal distress with diffuse muscle hypotonia, breathing and
swallowing difficulties, and facial diplegia with characteristic tenting of the
upper lips. Patients have a characteristic facial diplegia with
triangular-shaped "tented" mouth, and inability to close the eyes
fully. Death from respiratory failure is high. Myotonia is not elicitable at
birth and the diagnosis may be difficult to be made. Since most mothers are
affected, examination of the mother is helpful in establishing the diagnosis.
Histochemically, there is abnormal increase in acid phosphatase activity.
Genetics: The molecular mechanism and the gene involved is
the same as that of the adult type. These children are usually born to affected
mother, rarely affected father.
Muscle biopsy is not specific and not helpful diagnostically. It is more likely
to be confusing rather than helpful. Diagnosis is best based on genetic,
clinical, and EMG.
Clinical
features:
Polyhydraminios:
History of polyhydraminios is usually present.
Affected
mother: Mothers almost invariably show subclinical or
overt features of myotonic dystrophy. General hypotonia and difficulty with
sucking and swallowing and usually need tube feeding.
Onset: Symptoms usually starts at birth and is
characterized by neonatal distress with diffuse muscle hypotonia, breathing and
swallowing difficulties, and characteristic facial features. Arthrogyroposis or
talipes is often present.
Myotonia:
Myotonia is rarely elicitable before the age of two
and rare before the age of ten.
Characteristic
facial features:
Patients have a characteristic facial diplegia with triangular-shaped "tented" mouth, and inability to close the eyes fully.
Death from respiratory failure is high.
Clinical
course: patients show a gradual improvement in hypotonia
and will eventually walk, although considerably delayed. Myotonia is not a
feature of the newborn but if these patients survive long enough, myotonia will
eventually appear. Sucking, swallowing, and respiratory difficult may also
improve with time. Those who survive into adulthood develop a classic picture of
adult myotonic dystrophy.
Mental
retardation is
extremely common in congenital cases.
HISTOPATHOLOGY AND IMMUNOHISTOCHEMISTRY:
Head
Factors affecting the
histopathology: The histologic findings are age dependent; severe
changes are seen in those examined at early stages of disease. Biopsy obtained
by age 10 years may be almost normal. Histology also varies from muscle to
muscle and from case to case.
Features are similar to that of the adult type
characterized by ring fibers, sarcoplasmic mass, nuclear chains, and other
features. There are no degenerative changes.
Enzyme histochemistry: SDH and NADH-TR usually reveal a lack of enzymatic
activity in the peripheral zone of the fibers. Acid
phosphatase activity is abnormally high in this peripheral halo and persists
until the age of 6 years. Up to 80% of fibers may have acid phosphatase. This
feature is helpful in differentiating congenital myotonic dystrophy from
X-linked myotubular myopathy
and
congenital fiber disproportion syndrome.
Long survival: In patinets that survive to
adulthood, the histopathology is similar to classic cases.