Moebius Syndrome
Moebius 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. More about...181

Figure 164.1— Moebius syndrome. [A] At rest, no asymmetry is noted. [B] During crying, the facial asymmetry becomes obvious.

MRI abnormalities associated with Moebius syndrome include atrophy, brainstem hypoplasia, brainstem calcifications (Figure 164.2), and cerebellar atrophy.

A	B

Figure 164.2— MRI findings in Moebius syndrome. [A] Pontine atrophy. [B] Brainstem atrophy.

MRI 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.

A	B

Figure 164.3— MRI and CT of a patient with Moebius syndrome. [A] Normal. [B] Brainstem calcification.

PERIPHERAL NERVE

Congenital Hypomyelinating Neuropathy
Congenital 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.

Transient Congenital Myasthenia Gravis
Neonates 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.