Unusual Presentation of a Posterior Cerebral Artery Stroke

HISTORY AND PHYSICAL EXAMINATION A 79-yr-old man with history of type II diabetes mellitus, hypertension, hyperlipidemia, alcohol abuse, anxiety, depression, and chronic kidney disease presented to his primary care physician with 1-month history of lightheadedness, dizziness, and diarrhea. He was found to have a creatinine (Cr) level of 5.93 mg/dL. Repeat Cr level was 5.10 mg/dL 3 days later, and he was admitted to the hospital with increased confusion and inability to recognize familiar faces (prosopagnosia). He denied history of illicit drug use but vaped cannabidiol oil and started drinking liquor over the past 6–8 mos. Family history was significant for strokes in both parents. He was previously independent with activities of daily living and was literate. Vital signs were blood pressure 91/58 mm Hg, pulse 84 beats per minute, respiratory rate 18 breaths per minute, percent oxygen saturation 97%, and oral temperature 97.6°F. He was oriented to self and location but not situation, year, or current president. He spoke with short sentences without paraphasic errors. Repetition and comprehension were intact, but he was unable to name simple objects or distinguish colors. He read words aloud letter-by-letter and could not state the word’s meaning; however, he was able to write. He had a right homonymous superior quadrantanopia. Cranial nerves, strength, and sensation were intact. There was no pronator drift or abnormal movements. Finger tapping, heel-to-shin, and finger-to-nose tests were symmetric bilaterally. What Differential Diagnoses Should Be Considered? On neurologic examination, he was unable to read but still able to write, a finding called alexia without agraphia. Differential diagnoses are shown in Tables 1 and 2.2 Neurocognitive disorders were considered the most likely etiology. While this patient did have a history of depression, a psychiatric condition was ruled out given lack of psychiatric symptoms and presence of homonymous superior quadrantanopia. There was no history nor physical examination findings consistent with eye trauma, injury, cataracts, or blindness. Alcohol intoxication was considered given his history of alcohol abuse. He was not mute, making global aphasia less likely. TABLE 1 - Ophthalmologic and neurocognitive differential diagnosis and diagnostic modalities of alexia without agraphia Differential Diagnosis Physical Examination Pertinent Laboratory Results Imaging and Alternate Modalities Ophthalmologic causes Eye trauma/injury Gross abnormalities, visual acuity, ophthalmologic examination to include visual field deficits, extraocular movement Cataracts Ophthalmologic examination to include slit lamp examination of the fundus Blindness/visual field deficit Visual acuity Neurocognitive causes Stroke Detailed neurologic examination to include motor, sensory, visual-spatial, speech, cognition, swallowing disturbances General stroke laboratory results to assess secondary stroke prevention: lipid panel, hemoglobin A1c Head CT, brain MRI, echocardiogram, carotid duplex ultrasound Global aphasia Boston diagnostic aphasia examination, Western aphasia battery examination. Hearing test. General stroke laboratory results: lipid panel, hemoglobin A1c, PT/INR Head CT, brain MRI, echocardiogram, carotid duplex ultrasound Dementia MMSE, MoCA screening tools. Cognitive and neuropsychiatric evaluations assessing learning and memory, language, executive function, attention, perceptual-motor, social cognitive domains. Assess for neurologic deficits suggestive of stroke, parkinsonism, gait abnormalities, eye movements Vitamin B12 level, thyroid studies, RPR Head CT or MRI to rule out other etiologies Intoxication Vital signs, mental status, pupillary examination, neuromuscular examination Blood alcohol level, urine drug screen Multiple sclerosis McDonald criteria Lumbar puncture to assess for oligoclonal bands, ± autoantibodies Brain MRI, spine MRI; evoked potentials Migraine International Classification of Headache criteria Brain tumor Detailed neurologic examination to include motor, sensory, visual-spatial, speech, cognitive disturbances Brain MRI and/or head CT with and without contrast to look for tumor; tumor biopsy with histopathology, intracranial pressure History is a key component of diagnostics not to be excluded.MMSE, Mini Mental Status Examination; MoCA, Montreal Cognitive Assessment; PT, prothrombin time; RPR, rapid plasma reagin. TABLE 2 - Psychiatric and metabolic differential diagnosis and diagnostic modalities of alexia without agraphia Differential Diagnosis Physical Examination Pertinent Laboratory Results Imaging and Alternate Modalities Psychiatric causes Catatonia Bush-Francis Catatonia Rating Scale 1 CBC, Cr, kinase, iron Depression PHQ-9 to screen for depressive symptoms CBC, chemistry panels, TSH, RPR, hCG, UDS, urinalysis, Vitamin B12, folate, EKG to rule out other etiologies Schizophrenia DSM-5 diagnostic criteria Metabolic causes Hepatic encephalopathy Mental status LFTs, PT/INR, and serum ammonia level RUQ ultrasound and/or CT abdomen to look at liver morphology Syphilis Genital examination to look for skin abnormalities RPR B12 deficiency Detailed neurologic examination to include motor, sensory, visual-spatial, speech, cognitive disturbances, reflexes, extrapyramidal signs B12 level, CBC History is a key component of diagnostics not to be excluded.CBC, complete blood count; EKG, electrocardiogram; hCG, human chorionic gonadotropin; INR, international normalized ratio; LFTs, liver function tests; PHQ-9, Patient Health Questionnaire 9; PT, prothrombin time; RPR, rapid plasma reagin; RUQ, right upper quadrant; TSH, thyroid-stimulating hormone; UDS, urine drug screen. What Laboratory and Imaging Would Be Appropriate for Evaluation? Comprehensive laboratory workup was completed to evaluate this patient’s altered mental status. Basic metabolic panel showed a sodium level of 133 mmol/L (reference, 134–143), potassium 3.8 mmol/L (reference, 3.5–5.1), chloride 106 mmol/L (reference, 98–107), serum urea nitrogen 81 mg/dL (reference, 8–30), Cr 4.36 mg/dL (reference, 0.67–1.10), and glomerular filtration rate 13 mL/min/1.73 m2 (reference range, normal low 59). The patient’s baseline serum urea nitrogen, Cr, and glomerular filtration rate were estimated to be 30, 1.7, and 39, respectively. Renal ultrasound was normal. Urinalysis, urine drug screen, ethanol level, ammonia level, COVID-19, creatine phosphokinase, folate, lipid panel, hemoglobin A1c (5.4%), syphilis, and liver function panel were all normal. Vitamin B12 level was slightly elevated. A computed tomography (CT) of the head showed subtle hypodensity in the left posterior cerebral artery (PCA) area, overall atrophy, and moderate small vessel ischemic changes within the white matter; otherwise, no evidence of an acute infarct, hemorrhage, or mass lesion was noted (Fig. 1A). Magnetic resonance imaging (MRI) of the brain ultimately showed an acute to early subacute left PCA territory infarction (Fig. 1B) and a small acute to early subacute infarct in the right cerebellar hemisphere. Magnetic resonance angiography of the head and neck was within normal limits.FIGURE 1: A, Computed tomography head imaging showing a subtle hypodensity in the left PCA area (red arrow). B, An axial section of the MRI diffusion-weighted imaging sequence. The inferior-medial left occipital lobe and posterior-medial left temporal lobe infarcts are clearly seen as the area of hyperintensity on the MRI.DIAGNOSIS AND MANAGEMENT This patient’s alexia without agraphia was due to a PCA stroke damaging the visual word form area. He was discharged home on oral thiamine 100 mg daily, aspirin 81 mg daily, atorvastatin 20 mg daily, outpatient speech therapy, and outpatient Holter monitor. The Holter monitor did not find arrhythmia, and the etiology of stroke was cryptogenic. He was referred to occupational therapy for vision rehabilitation. He was recommended to follow up with neuro-ophthalmology and outpatient physiatry, but he did not attend those visits. Three months after his discharge from acute care, his neurology follow-up documentation revealed persistent prosopagnosia, peripheral vision was absent, alexia without agraphia, and the inability to know what he was writing. He completed three sessions of speech therapy with improvements noted in recent memory and/or general knowledge and compliance with memory strategies at home. DISCUSSION Alexia without agraphia, also known as pure alexia or occipital/posterior alexia, is usually accompanied by right-sided homonymous hemianopia, as seen in this patient. While there are other etiologies of alexia without agraphia, such as acute encephalopathy, multiple sclerosis, or glioblastoma, most cases of pure alexia are due to a left (dominant) PCA stroke damaging the medial occipitotemporal gyrus, also known as the visual word form area.3 Alexia without agraphia is an uncommon presenting symptom after stroke. Posterior cerebral artery strokes comprise only 5%–10% of all strokes, and strokes causing pure alexia are even rarer. The incidence of pure alexia is difficult to determine because it is mostly discussed in case studies in the literature. The clinical presentation of PCA strokes is often highly variable, nonspecific, and may be fluctuating in nature, making the diagnosis challenging.4 The case presented with occipital alexia. Occipital alexia differs from other acquired alexias, such as central or parietooccipital alexia, anterior, or frontal alexia, due to the lack of hemisensory neglect and retained ability to write.4 This patient retained the ability to distinguish individual letters, spell, and write, but he could not identify words or comprehend their meaning. Each acquired alexia is caused by a different anatomic lesion. The PCA has four segments. P1 and P2 are the proximal segments of the artery and supply the midbrain, whereas P3 and P4 are the distal segments of the artery and supply the temporal and occipital lobes, respectively.4 The neuroanatomical area that controls visual perception and interpretation is known as the visual word form area, located in the occipitotemporal gyrus.3 In patients with pure alexia, visual input from the intact right visual cortex cannot be relayed to the left angular gyrus. The language comprehension areas of the brain where the visual word form area is located as well as splenium of the corpus callosum are also damaged.3 The patient retains the ability to spell and interpret words spelled out to them because the communicating area between the auditory centers and the language centers is maintained.5 The patient maintains the ability to write as the left angular gyrus remains intact due to blood supply from the middle cerebral artery; it is the connection pathway that is destroyed, not the angular gyrus itself.3 The association with a contralateral visual field defect resulting in hemianopia, most often on the right, is due to damage to the left visual cortex.3 Our patient presented with right superior quadrantanopia, which occurs when the calcarine artery (supplied by the superficial/distal PCA), is affected.4 Clinically, assessing reading comprehension, writing ability, visual acuity, and visual fields are important to aid in diagnosis. With regard to imaging, MRI is the criterion standard for diagnosis, because CT scans can miss acute ischemia or small subcortical strokes. Diffusion-weighted imaging sequence is the most sensitive sequence to identify acute infarcts. Management and prognosis largely depend on the severity of the patient’s symptoms and capitalizing on those abilities the patient retains. In this case, this patient was not a candidate for tissue Plasminogen Activator as his last known well time was over 48 hrs before hospital admission; he was also not a candidate for endovascular therapy given the lack of large vessel occlusion on imaging. Speech therapy was important for neurocognitive recovery. For individuals with intact letter recognition, a letter-by-letter approach is used in which each letter is sounded out individually.1 For individuals with intact writing skills, the patient will trace the letters and sound them out by the tactile input provided from writing the letter.1 As with any rehabilitation, these tactics must be used regularly to increase reading speed over time, but a definitive cure has not been found.1 Based on this patient’s cognitive impairments, 24/7 supervision and oversight of instrumental activities of daily living would be appropriate. Although full discussion of different presentations of PCA strokes could not be covered here, it is important to recognize this unique presentation of alexia without agraphia associated with homonymous hemianopia as a potential stroke. Given the variable presentation and wide range of anatomical areas affected in PCA strokes, having a keen eye for subtle findings can be the difference in quickly diagnosing a stroke. This patient presented with acute kidney injury and chronic diarrhea, which could serve as distractors from making the diagnosis of a PCA stroke. We must remain vigilant in assessing all symptoms, no matter how subtle they may be. Exempt status for this clinical vignette was obtained from the institutional review board. This study conforms to all CARE guidelines and reports the required information accordingly (see Supplemental Checklist, Supplemental Digital Content 1, https://links.lww.com/PHM/B672).

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