Description: My attention is drawn to the minimal ptosis of the right eye in Figure 5.1A. I do not see an obvious palsy in Figure 5.1A, in fact the light reflex is normal in primary gaze. On the other hand, of importance, there is retraction of the right upper lid in Figure 5.1B in downward gaze. There is some type of aberrant regeneration of the third nerve palsy based on limitation of depression of the right eye with coupled retraction of the upper and lower right lids.

Differential Diagnosis: Given the history of a previous third nerve palsy, this is likely a form of third nerve palsy such as a partial, complete, or aberrant with or without pupil involvement. Given this patient’s history and current presentation, I am inclined toward the diagnosis of a compressive injury from the previous aneurysm or aberrant regeneration secondary to the initial insult or surgery. In general, other conditions that can present with third nerve palsies without a particular neurologic pattern include orbital disease (orbital fracture, orbital cellulitis, orbital malignancy), systemic disease (myasthenia gravis, Eaton-Lambert syndrome), neuro-ophthal-mologic (aberrant regeneration of third nerve, demyelination of third nerve, vestibular-ocular disease), and vascular etiologies (third nerve infarct, aneurysm compression).

History: In this case, I want to know the following: What symptoms did the patient have at initial presentation of his PCA aneurysm? How long did the patient have diplopia? Is the patient experiencing vision loss? Does he have any difficulty with eye movement? Has the onset of current symptoms been sudden or gradual? Is there any eye pain or facial pain?

Exam: The first and most important aspect of my evaluation is to assess pupillary response for afferent pupillary defect (APD). Given the patient’s history and likely third nerve aberrant regeneration, pupil abnormalities with eye movement are to be expected and may not be as alarming as the initial presentation. I would proceed with a complete neurologic examination, cranial nerve examination, and ocular examination evaluating ocular motility, visual fields, ptosis, and proptosis in both eyes. This examination would likely demonstrate lid retraction with downward gaze highly associated with aberrant regeneration. The patient’s difficulty with upward gaze would also be indicative of this condition.

Workup: I would order central nervous system (CNS) imaging particularly as aberrant regeneration secondary to PCA aneurysm correction is suspected in this case. I do not suspect myasthenia gravis, but in such cases, edrophonium chloride testing is helpful to rule out new-onset M.G. Patients with a risk factor for giant cell arteritis need erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and platelets.

Treatment: I would make sure the patient’s other health conditions that contributed to third nerve palsy worsening are well managed such as the PCA aneurysm, diabetes mellitus, and hypertension. This patient’s condition is commonly refractive to surgical correction, so I would prescribe prisms for near or distance vision, if diplopia was present.

Advice: With appropriate workup, I would reassure the patient that this is a possible sequela of his injury from previous PCA aneurysm.

Follow-up: After ruling out any urgent etiologies, I would follow this patient initially every 4 to 6 months to ensure that the condition is stable and not developing any new aberrations or palsies.

Description: My attention is drawn to the left eye hypertropia in this patient’s primary gaze.

Differential Diagnosis: In the setting of new-onset diplopia and strabismus, my differential diagnosis is a cranial nerve palsy. Because in this presentation the left eye is hypertropic and the patient has worse diplopia on right gaze, a left fourth nerve palsy is my number one working diagnosis. The real concern is what the etiology is in this apparently healthy patient. Causes of acquired fourth nerve palsies include trauma (orbital fracture, Brown syndrome, postocular surgery), neurologic (M.S., incomplete third nerve palsy, diabetic neuropathy), systemic (myasthenia gravis, thyroid eye disease), and vascular (hypertension [HTN], giant-cell arteritis, aneurysms) etiologies. Most commonly, a vascular infarct from underlying diabetes and HTN are the causes.

History: I would ask the patient whether this condition has occurred in the past, as this could be a congenital fourth nerve palsy that has decompensated. What is his past medical history? Is there any pain associated with eye movement? Has there been any recent head trauma or recent stroke? Has he had any recent surgeries? Does head tilt help? Old photographs are useful in looking for chronic head tilt the patient may not have noticed.

Exam: I would be especially focused on visual field and gaze assessments. I would perform the three-step test in order to confirm that this is an isolated fourth nerve palsy. Firstly, I would use the cover/uncover to determine which eye is deviated upward in primary gaze. Secondly, I would determine the lateral gaze in which the deviation is greatest. Finally, I would see which direction of head tilt produces the greatest deviation. An isolated fourth nerve palsy would show hyperdeviation worse when the dysfunctional eye is directed nasally and head tilt to the ipsilateral shoulder. I would also perform the double Maddox rod test to confirm this diagnosis.

Workup: The goal of workup is to determine the underlying cause, especially in such a young patient. Therefore, I would consider MRI and computed tomography of the head to evaluate for orbital disease, mass effect, and intrinsic neurologic abnormalities. I would obtain blood pressure measurement, fasting glucose, and HgA1c levels to evaluate for vascular and diabetic neuropathy. In older patients, I order ESR, CRP, and platelets to rule out giant cell arteritis, especially in the setting of pain.