by Ana Sruk, Hrvoje Budinčević, Ivan Bielen
We present a 70-year-old woman whose symptoms started in the afternoon hours 3 days before hospital admission, with a sudden onset of vertigo followed by excessive daytime sleepiness and extended sleep period. The next morning, the patient started to experience diplopia when gazing to the distance, especially upwards and downwards.
In the previous medical history we found that two months earlier she had started to take drugs for treatment of hypothyreosis. She was followed up by a cardiologist under the diagnosis of pectoral angina, arterial hypertension and hyperlipidemia. In April 2008 triple coronary bypass surgery had been performed due to subtotal stenosis of the left coronary artery and obliteration of the right coronary artery.
She also has bilateral chronic glaucoma; cataract surgery had been performed on the right side, while for the left eye, surgery was planned for the near future. She was taking acetylsalicylic acid, combination of ACE-inhibitor and diuretic, beta-adrenergic blocking agent, hipolipemic agent, levothyroxine and antiglaucoma eye drops on a regular basis.
Neurological and physical examination showed only a slight delay of left bulbus when gazing to the left-lower direction and facilitated miotatic reflexes, especially the patellar reflex till subclonus. Initially, in the emergency department, a multislice computed tomography (MSCT) of the brain was performed and showed bilateral thalamic hypodensities, more on the right side, described by the radiologist as chronic vascular lesions (Figure 1). Ultrasound of the carotid and vertebral arteries (CDFI) showed a soft plaque with moderate degree hemodynamic stenosis (ca. 55-65%) of left internal carotid artery (ACI) and reduced left ophthalmic artery (AO) flow (Figure 2). The patient was admitted to hospital and extensive diagnostics were performed. Laboratory exams were mainly within range values; we found only slightly elevated values of D-dimers (782µg/L) and uric acid (408µmol/L). The lipidogram showed mildly elevated values of triglycerides (1.76mmol/L) with normal values of cholesterol. Triiodothyronine (T3) values were slightly decreased (1.32nmol/L) while the values of tetraiodothyronine (T4) and thyroid-stimulating hormone (TSH) were normal. Because of the sinus bradycardia (53 beats per minute) recorded in the electrocardiogram, the cardiologist recommended reducing the dose of beta-adrenergic blocking agent. Also, due to lower values of arterial pressure registered during the hospitalization, the dose of the antihypertensive agent (combination of ACE-inhibitor and diuretic) was reduced by half. The chest X-ray was insignificant showing only an increased heart silhouette of aortal configuration. Magnetic resonance imaging (MRI) of the brain revealed an acute ischemic infarction lesion (size 10-15 millimetres) of the area around the third ventricle – posterior in the thalamic and hypothalamic regions, together with multiple vascular lesions of different time genesis (bilateral para- and periventricular subcortical frontoparietal) (Figure 3). MRI of the cervical spine showed multiple degenerative changes of intervertebral discs, with an intact spinal medulla. MSCT angiography confirmed stenosis of the left ACI (ca. 55%) (Figure 4). The results of visual evoked potentials were normal. Ophthalmologic examination and Hess–Lancaster test supported the diagnosis of left isolated inferior rectus palsy (Figure 5). The patient was discharged on the 13th day; on follow up visits, the patient has been reporting a gradual reduction of the diplopia.
Ana Sruc and colleagues are working at the Stroke and intensive care unit of the department of Neurology at the University Hospital “Sveti Duh” in Zagreb, Croatia
Comment by the authors
According to data from available literature, the most common causes of isolated inferior rectus palsy are of vascular and traumatic etiology. Vascular causes include microvascular ischemia, cerebral infarction and dural arteriovenous fistulas. Not so often, isolated inferior rectus palsy could be a symptom of myasthenia gravis, endocrine (for example, disthyreoid) myopathy, inflammatory diseases and other orbital diseases (for example, tumours) (1-7). Lesions could be central (nuclear and fascicular) and peripheral (neuropathic) (1).
In our patient, we observed most probably, a vascular cause of isolated inferior rectus palsy, most likely central, but without an absolute possibility of excluding a peripheral cause. Till now, midbrain infarction (2,3) and paramedian thalamopeduncular infarction (4) have been described as examples of central lesions which may cause isolated inferior rectus palsy. Unfortunately, because of the dimension of the bilateral thalamic and hypothalamic lesions, we cannot precisely determine which of the affected structures might be responsible for the observed neurological deficit. Furthermore, we could also question whether there is a symptomatic stenosis of the left ACI which may have, together with bradycardia and possible arterial hypotension, precipitated the hemodynamic infarction. This hypothesis has been taken under our consideration due to known individual, numerous and complex anatomical variations of arterial irrigation of the thalamic area (7). As a possible peripheral cause, there is ischemic peripheral neuropathy, caused by reduced AO flow (1). Extreme variability of arterial irrigation of the extraocular rectus muscles has been described, but most of the muscle branches are supplied from different branches of the AO (in the case of inferior rectus, from the inferior muscular artery) (9).
Based on the clinical feature of sudden onset of diplopia preceded by vertigo and excessive daytime sleepiness (maybe even somnolence), in a patient with high cardio- and cerebrovascular risk factors, we concluded that most likely these were the symptoms of stroke, supported by neuroradiological findings. Nevertheless, regarding the extremely rare presentation of isolated inferior rectus palsy, a wide differential diagnosis and incompletely clarified mechanisms of genesis, we chose this case report for the Grand Round section. Additionally, we would like to encourage all the readers and appreciated experts in discussing, whether this is actually a case of symptomatic stenosis and should a surgical or eventually endovascular treatment of carotid disease be considered.
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