Typical microvascular third-nerve palsy requires checklist

La Jolla, CA-When diagnosing a cranial third-nerve palsy, there are a number of factors to consider that let the ophthalmologist decide whether a patient's third-nerve palsy is microvascular, or whether the cause is a more serious one. Leah Levi, MBBS, described the checklist that she uses to arrive at the diagnosis of microvascular third-nerve palsy.

She recounted the case of a 65-year-old woman with diabetes who had acute onset of unilateral pain, diplopia, and ptosis, and was found to have a unilateral third-nerve palsy. The differential diagnosis included tumor, infection, stroke, microvascular third-nerve palsy, or a posterior communicating arterial aneurysm.

"The bottom-line clinical problem is to determine if the patient needs urgent neuroimaging or other investigations," said Dr. Levi, clinical professor of ophthalmology and neurosciences, University of California, San Diego, La Jolla, CA. "The question to be answered is: Does the patient have a typical presentation of a microvascular third-nerve palsy or not? If the presentation is atypical, investigation is obligatory.

Dr. Levi described her checklist for typical cases: patient age of 50 years or older; a vasculopathic history; the presence of pain; acute onset; the absence of other neurologic or cranial nerve involvement; a unilateral picture; and evolution to a complete third-nerve palsy sparing the pupil.

"If all these factors apply, I am comfortable that the patient has a microvascular third-nerve palsy," she said.

But the patient must be followed for 3 months to see improvement and complete resolution, she added.

Dr. Levi pointed out the red flags to be aware of that would make it less likely that the patient had a "typical" microvascular third-nerve palsy.

"Younger patients might develop a microvascular third-nerve palsy if there has been a longstanding vasculopathic history," she said. "However, generally if the patients are too young, I examine them for other causes of microvascular third-nerve palsy."

These other pathologies include vasculitis, blood dyscrasias, coagulopathies, or paraproteinemias. In addition, if the patient satisfies all the criteria of a typical presentation of microvascular third-nerve palsy, but there is no history of vasculopathy, Dr. Levi suggested further evaluation by the patient's primary-care physician to look for underlying vascular risk factors.

Pain, she noted, is not a helpful symptom, because most of the microvascular third-nerve palsy cases are painful, as are the compressive third-nerve palsies.

"The location and the severity of the pain do not help the clinician," she said.

She advised that microvascular third-nerve palsy has an acute onset. A patient who presents with a chronic progressive case has a different condition.

"A critical issue is that the microvascular third-nerve palsy must be isolated, so the clinical checklist includes evaluation of the orbit, the visual system, and other cranial nerves," she said. "Patients who present with a hemiplegia should not have a microvascular third-nerve palsy diagnosed."

The patient should have no proptosis, congestion, pain on eye movement, or other cranial neuropathies. Clinical work-up should include measurement of visual acuity, visual fields, identification of an abduction deficit to look for sixth-nerve involvement, examination for intorsion of attempted downgaze to evaluate the fourth nerve, and evaluation of trigeminal function, according to Dr. Levi.

The clinician should also rule out signs and symptoms associated with midbrain pathology, neuromuscular signs such as variability, fatigability, bilaterality, or weakness of the orbicular muscle.

An important factor when looking for microvascular third-nerve palsy is that the condition is unilateral.