A rare genetic myopathy presenting at birth with
hypotonia and muscle weakness. Findings occurring later
in life include short stature, progressive scoliosis, hip dislocation, and
deformities of the feet.
Congenital Fiber-type Disproportion Myopathy.
The exact incidence of
congenital myopathies is unknown, however, congenital myopathy with
fiber-type disproportion (CMFTD) seems to account for approximately 20%
of cases. Autosomal recessive transmission is the most common form; however,
autosomal dominant inheritance and sporadic cases have been described.
Genetic heterogeneity is probable.
CMFTD can be found in other forms of congenital
myopathy and other diseases (e.g., Duchenne Muscular Dystrophy,
Spinal Muscular Atrophy Syndrome, metabolic myopathies, central nervous system
diseases such as leukodystrophies, Lowe Syndrome, and Moebius
Syndrome); however, it also exists as a distinct diagnostic entity.
Generalized hypotonia and weakness are noticeable at birth, and failure to
thrive is common. The prognosis is often good because the disease is
usually not progressive. In some cases, improvement with age has been
reported. However, in approximately 25% of patients, the course is
severe, with death resulting from respiratory failure in approximately
10% of patients. Skeletal involvement is common and may present with
short stature, (kypho)scoliosis, contractures, joint laxity, and congenital
hip dislocation. Bulbar palsy and ophthalmoplegia are less common and
associated with a poor prognosis. Cardiac involvement (dilated
cardiomyopathy, arrhythmias) is rare, but can be significant and require
medical treatment or even heart transplant. In a minority of these patients,
facial anomalies (e.g., high arched palate) and insulin-resistant diabetes
mellitus have been reported. The diagnosis is confirmed by muscle biopsy,
which commonly shows small, atrophic type I fibers and compensatory
hypertrophic type II fibers. In CMFTD, type I fiber mean diameter should
be at least 12% smaller than that of type II fibers, although some groups
consider a difference of 25% more appropriate. Rarely, a small number of
type I fibers shows signs of hypertrophy.
This disease requires a complete workup,
including assessment of neurologic and motor milestones, family history, and
past medical history. Respiratory function should be checked preoperatively
(e.g., chest radiographs, arterial blood gas analysis, pulmonary function
tests), and preoperative physiotherapy likely will be beneficial.
Nevertheless, one should be prepared for prolonged postoperative mechanical
ventilation. Regular and close monitoring of blood glucose in the
perioperative period is recommended. Scoliosis not only may make airway
management more difficult but also may lead to restrictive lung disease and
cor pulmonale. A rapid-sequence induction technique should be considered in
the presence of bulbar symptoms. Patient positioning may be difficult but
must be done with great care because joint laxity with dislocation (hip) is a
common problem in these patients. Because cardiac problems have been
described in some of these patients, the threshold for a cardiac consult
and/or echocardiography should be low. In case of cardiac anomalies, invasive
monitoring is recommended. Regional anesthesia per se is not
contraindicated, however, positioning problems and scoliosis can affect the
success rate negatively ...