syndrome consists of bilateral facial weakness and inability to abduct
the eyes. Moebius syndrome is due to dysfunction of cranial nerves VI
and VII motor units (Figure 164.1). The dysfunction may be due to hypoplasia
or destruction of the cranial nerve motor neurons, nerve abnormalities,
or muscle pathology. Other cranial nerves abnormalities may be present
such as atrophic changes of the tongue due to cranial nerve XII involvement.
Poland sequence may occur in association with Moebius syndrome. Arthrogryposis
is present in about one-third of patients with Moebius syndrome. Mental
deficiency is present in 15% of cases. Moebius syndrome is usually sporadic.
Ingestion of Misoprostol during pregnancy may produce Moebius syndrome.
A dominant transmission is present in some cases.
Figure 164.1— Moebius syndrome.
[A] At rest, no asymmetry is noted. [B] During crying, the facial asymmetry
abnormalities associated with Moebius syndrome include atrophy, brainstem
hypoplasia, brainstem calcifications (Figure 164.2), and cerebellar
Figure 164.2— MRI findings
in Moebius syndrome. [A] Pontine atrophy. [B] Brainstem atrophy.
may not detect calcifications of the brainstem. CT scan is more sensitive
for detection of calcifications (Figure 164.3).
Hence, patients with Moebius syndrome should have both studies if an
ambormality is not detected in the first modality used.
Figure 164.3— MRI and CT of
a patient with Moebius syndrome. [A] Normal. [B] Brainstem calcification.
hypomyelinating neuropathy is a rare cause of arthrogryposis. Neonates
are hypotonic and weak. Nerve conduction studies reveal a reduced motor
conduction of 5 to 8 meters per second. The diagnosis is established by
sural nerve biopsy. Sural nerve biopsy shows a minute amount or absence
of myelin sheaths and occasional onion-bulb formation.
Congenital Myasthenia Gravis
with transient myasthenia gravis may have arthrogryposis. They also have
hypotonia, weakness, and fatigability. Fatigability is the hallmark of
myasthenia gravis. The diagnosis is established by evaluating the mother.
Mothers of neonates with transient congenital myasthenia gravis have a
history of myasthenia gravis or have clinical findings of myasthenia gravis.
Treatment with neostigmine improves strength. Physical therapy is effective
to relieve contractures.