What causes trochlear nerve palsy (fourth nerve palsy)?

Updated: Oct 08, 2019
  • Author: Zafar A Sheik, MD, MD; Chief Editor: Andrew G Lee, MD  more...
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The most common cause of congenital trochlear nerve palsies is congenital cranial dysinnervation syndrome, followed by an abnormal superior oblique tendon. [8, 9, 10]

The most common cause of acquired isolated fourth nerve palsy, after idiopathic, is head trauma. [11, 12, 13]

One must consider the possibility of underlying structural abnormalities (eg, skull based tumor) if fourth nerve palsy results after only minor trauma.

Microvasculopathy secondary to diabetes, atherosclerosis, or hypertension also may cause isolated fourth nerve palsy. [14]

There are rare reports of thyroid ophthalmopathy and myasthenia gravis mimicking an isolated fourth nerve palsy. These patients eventually develop other findings, unmasking the underlying diagnosis.

Tumor, aneurysm, multiple sclerosis, or iatrogenic injury may present with isolated fourth nerve palsy that may evolve over time to include other cranial nerve palsies or neurologic symptoms. [15]

Fourth nerve palsy may become manifest after cataract surgery. Patients with underlying, well-controlled, and asymptomatic fourth nerve palsy may decompensate gradually as they lose binocular function resulting from cataract. Following restoration of good vision, these patients become aware of diplopia.

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