Diffusion-Weighted Magnetic Resonance Imaging of Porphyric Encephalopathy: A Case Report

Acute intermittent porphyria is an uncommon metabolic disease with cerebral manifestations. Acute porphyric encephalopathy can be difficult to differentiate from arterial ischemic stroke, owing to polymorphism in its clinical presentation [1]. Here we describe a patient with acute intermittent porphyria (AIP) with the clinical presentation as cortical blindness. Magnetic resonance (MR) imaging showed T2 hyperintense lesions in the bilateral frontal and occipital areas. Diffusion-weighted MR imaging (DWI) suggested these hyperintensities were due to vasogenic edema instead of cytotoxic edema. Vasogenic edema may be the basis for the pathophysiology of porphyric encephalopathy. To our knowledge, DWI of the acute phase of porphyric encephalopathy has not yet been reported. Case Report A 25-year-old woman was admitted to our hospital in February 1998, having suffered acute-onset loss of vision and severe headache for 1 day. On admission, she was apyretic, with a blood pressure of 180/100 mm Hg, and a regular pulse of 84/min. She had suffered from chronic abdominal pain and bilateral leg soreness for several weeks prior to admission. The physical examination was unremarkable. Neurologic examination disclosed bilateral blindness with mild cognitive dysfunction. The remaining cranial nerves were intact. Pinprick sensation and muscle power of the extremities were normal. A noncontrast CT scan of the brain showed subtle areas of low density in the bilateral occipital lobes. Subsequent T2-weighted MR imaging showed areas of hyperintensity in the bilateral occipital lobes (fig. 1). Blood biochemistry revealed slightly elevated GOT and GPT. Tests for antinuclear and anticardiolipin antibodies were normal. Muscle biopsy was normal. Assuming polyarthritis, top of basilar artery syndrome and hypertension, corticosteroid, heparin and antihypertensive medications were instituted. With the gradual improvement of her vision, the patient was discharged 2 weeks later. However, in June 1998, she was readmitted due to severe abdominal pain, nausea, vomiting and loss of vision. Her consciousness was drowsy with a blood pressure of 170/110 mm Hg. An episode of general tonicclonic convulsion developed on the second day and antiepileptic agents were administered. Follow-up MR imaging was performed on a 1.5-tesla Magnetom Vision whole-body scanner (Siemens, Erlangen, Germany) with echo-planar capabilities. DWI and apparent diffusion coefficient (ADC) maps were obtained using single-shot echoplanar imaging with a repetition time (TR) of 2,682 ms, echo time (TE) of 135 s, field of view of 265 mm, image matrix of 80 ! 128, slice thickness of 6 mm with a 5-mm gap and 12 axial slices. The b-values were 0 and 900 s/mm2 with diffusion gradients applied simultaneously in three orthrogonal spatial directions corresponding to read, slice and phase-encoded directions. Calculation of the ADC was based on the Stejskal and Tanner equation and ADC maps were created on a pixel-by-pixel basis [2]. MR imaging studies revealed multiple hyperintensities on long-TR images in bilateral frontal, parietal and occipital cortical and subcortical areas. DWI and calculated ADC map revealed increased values in the involved areas suggesting a vasogenic edema pattern (fig. 2) Complete 4-vessel cerebral angiography disclosed no evidence of a vascular lesion or vessel