Genetic disorder consisting of a benign congenital
myopathy and contractures.
Benign Congenital Muscular Dystrophy.
Unknown. Since the original report of the condition in
1977 by J. Bethlem and G.K. Van Wijngaarden, the myopathy has been described
in at least nine pedigrees from various geographical locations, including
the Netherlands, Poland, and Canada. The largest pedigree with the disorder
was of French-Canadian ancestry in which the disease was traced back through
Autosomal dominant. Gene map locus is most
often 21q22.3, but in some patients is 2q37, suggesting a locus
heterogeneity within Bethlem myopathy.
Genetic linkage studies suggest Bethlem myopathy
is caused by mutations in the genes encoding the three constituent α-chain subunits of type VI collagen. Microfibrillar type VI collagen is
believed to play a role in bridging cells with the extracellular matrix.
Made by clinical features consistent with the condition.
Electromyography demonstrates a myopathic pattern. Muscle biopsy reveals nonspecific
features of a myopathy. Nerve conduction is normal, and creatinine
phosphokinase serum levels are normal or mildly elevated.
Characterized by a benign limb girdle myopathy
with mild-to-moderate weakness and wasting of muscles. Onset is in early
infancy or childhood (age 2-5 years) with a benign course and slow
progression, leaving some of the affected patients only minimally impaired
in old age. However, many patients require a wheelchair after 50 years of age,
and some die of respiratory failure as a consequence of progressive
respiratory muscle weakness, particularly of the diaphragm. Proximal and
extensor muscles are more affected than distal and flexor muscles. Early
flexion contractures involve the elbows, ankles, interphalangeal joints of
the last four fingers, and planta pedis. Congenital torticollis may be
present. Cardiac and respiratory involvement usually is not a feature of
Detailed clinical history and
examination are required to determine the exact nature of the myopathy and
the progression of the condition. Evaluate the severity of any flexion
deformities and congenital torticollis. Obtain family history of previous
anesthetic complications (hyperthermic response). Blood work should include
creatinine phosphokinase and electrolytes.
Airway management, including direct
laryngoscopy and tracheal intubation, may be difficult in the presence of
fixed flexion deformities of neck muscles or congenital torticollis (awake
fiberoptic intubation or inhalational induction in children followed by fiberoptic intubation may be required).
Positioning and venous access may be difficult because of flexion
deformities. Although congenital myopathies have been associated with
malignant hyperthermia, the evidence supporting this causal relationship is
poor. No case reports of malignant hyperthermia reaction in Bethlem myopathy
have been published. Nevertheless, caution should be exercised when using
known trigger agents, and full monitoring (including core and peripheral
temperature) should be used in the perioperative period. Depending on the degree of muscle
weakness and the procedure, postoperative mechanical ventilation may be required.
Avoidance of known trigger agents may
be advisable until more information about the condition is ...