This retrospective study used an electronic medical record system to identify all cases of isolated fourth nerve palsy diagnosed from January 1, 2009, through July 31, 2020 at Ramathibodi Hospital, Thailand, a tertiary referral center.
The study protocol was approved by the Human Research Ethics Committee Faculty of Medicine Ramathibodi Hospital, Mahidol University and adhered to the tenets of the Health Insurance Portability and Accountability Act and the Declaration of Helsinki.
Patients
Unilateral isolated fourth nerve palsy was defined as incomitant hypertropia, underaction of the superior oblique muscle with or without overaction of inferior oblique muscle, positive unilateral head tilt test or excyclotorsion with the double Maddox rod test less than 10 degrees. Fundus photography was performed to confirm affected eye excyclotorsion.
Bilateral isolated fourth nerve palsy was defined as underaction of bilateral superior oblique muscle with or without overaction of bilateral inferior oblique muscle, alternating hypertropia on horizontal gaze or tilt, positive bilateral head tilt test, excyclotorsion with the double Maddox rod test more than 10 degrees or a V-pattern esotropia of greater than 25 prism diopters. Fundus photography was performed to confirm bilateral excyclotorsion.
Exclusion criteria for all patients were: a history of orbital disorders; myasthenia gravis; multiple cranial nerves disorders; and nuclear and supranuclear disorders with other paretic or restrictive causes.
All patients' medical records were reviewed, to confirm their diagnosis, and to identify the medical conditions and etiologies of the isolated fourth nerve palsy. We recorded the following: demographic data, age at presentation, and the etiologies of isolated fourth nerve palsy. Not every case was confirmed the diagnosis by neuroimaging. Atypical presentations of fourth nerve palsy, such as rapidly progressive diplopia, profound headache, ptosis, periocular pain, ataxia with positive cerebellar signs, and painful eye movements were investigated by neuroimaging, and reviewed.
Classification Of Etiologies Of Isolated Cranial Palsy
Congenital fourth nerve palsy was diagnosed based on the infant’s photographs with facial asymmetry, or on a history of vertical misalignment or abnormal head posture, presence of large vertical fusional amplitudes (more than 5 prism diopters)6,7 and absence of subjective torsion.
Traumatic fourth nerve palsy was defined as the presence of fourth nerve palsy following head trauma.
Vasculopathy was defined as medical hypertension, diabetes mellitus, dyslipidemia, or a combination thereof, measured within 1 year before or after the onset of isolated fourth nerve palsy and requiring management. Laboratory investigations (complete blood count, fasting blood glucose and lipid profile) were performed. Hypertension was diagnosed using the criteria of the Eighth Report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure, that is, systolic or diastolic blood pressure elevated to more than 140/90 mm Hg on presentation.8 Diabetes mellitus was defined using the 2020 American Diabetes Association criteria.9 The criterion for a diagnosis of dyslipidemia was the presence of at least one of the following: more than 200 mg/dL total cholesterol, more than 130 mg/dl of low-density lipoproteins, or more than 150 mg/dL of triglycerides.10 Patients with vasculopathy were followed, and their diagnosis confirmed, when ocular misalignment resolved within 6 months.
Intracranial neoplasm was diagnosed if the isolated fourth nerve palsy was a direct result of a neoplasm identified based on clinical symptoms and neuroimaging.
Other etiologies in our study included post-neurosurgery causes, arterovenous malformation (AVM), brain aneurysm and hemorrhagic stroke.