Post-transplant acute limbic encephalitis: clinical features and relationship to HHV6

BACKGROUND

Acute limbic encephalitis has been reported in the setting of treatment-related immunosuppression and attributed to human herpesvirus-6 (HHV6) infection. Clinical and laboratory features of the syndrome, however, have not been well characterized.

METHODS

We describe the clinical, EEG, MRI, and laboratory features of nine patients with acute limbic encephalitis after allogeneic hematopoietic stem cell transplantation (HSCT). To explore the relationship between HHV6 and this syndrome, we reviewed available CSF HHV6 PCR results from all HSCT patients seen at our center from March 17, 2003, through March 31, 2005.

RESULTS

Patients displayed a consistent and distinctive clinical syndrome featuring anterograde amnesia, the syndrome of inappropriate antidiuretic hormone secretion, mild CSF pleocytosis, and temporal EEG abnormalities, often reflecting clinical or subclinical seizures. MRI showed hyperintensities within the uncus, amygdala, entorhinal area, and hippocampus on T2, fluid-attenuated inversion recovery (FLAIR), and diffusion-weighted imaging (DWI) sequences. CSF PCR assays for HHV6 were positive in six of nine patients on initial lumbar puncture. All patients were treated with foscarnet or ganciclovir. Cognitive recovery varied among long-term survivors. The one brain autopsy showed limbic gliosis and profound neuronal loss in amygdala and hippocampus. Among 27 HSCT patients with CSF tested for HHV6 over a 2-year period, positive results occurred only in patients with clinical limbic encephalitis.

CONCLUSIONS

Patients undergoing allogeneic hematopoietic stem cell transplantation are at risk for post-transplant acute limbic encephalitis (PALE), a distinct neurologic syndrome. Treatment considerations should include aggressive seizure control and, possibly, antiviral therapy. PALE can be associated with the CSF presence of human herpesvirus-6, but the pathogenic role of the virus requires further exploration.

Pathogenetic role of 1 alpha,25-dihydroxyvitamin D in sarcoidosis and absorptive hypercalciuria: different response to prednisolone therapy

Intestinal hyperabsorption of calcium (Ca) is frequently observed in sarcoidosis and is characteristic of absorptive hypercalciuria (AH). The potential pathogenetic role of 1 alpha,25-dihydroxyvitamin D [1,25(OH)2D] in these two conditions was sought by a careful assessment of the circulating concentration of this vitamin D metabolite and various measures of Ca metabolism before and after prednisolone therapy. In eight patients with sarcoidosis, prednisolone treatment (50 mg/day for 8 days) produced a significant fall in serum 1,25(OH)2D [4.8 +/) 1.9 to 3.3 +/- 1.0 (SD) ng/dl; P less than 0.025], concomitant with a significant decrease in the fracitional intestinal Ca absorption (alpha) from 0.58 +/- to 0.14 to 0.46 +/- 0.13 (+/- SD; P less than 0.005). Urinary Ca and serum parathyroid hormone did not change significantly. However, in six patients with AH, prednisolone therapy resulted in a nonsignificant rise in serum 1,25(OH)2D from 3.6 +/- 0.7 to 4.4 +/- 1.0 ng/dl and no significant fall in alpha (from 0.73 +/- 0.08 to 0.70 +/- 0.10). Urinary Ca was significantly increased in AH patients from 230 +/- 35 to 343 +/- 74 (SD) mg/day (P less than 0.005), while serum parathyroid hormone rose slightly. Serum 1,25(OH)2D and alpha were significantly correlated (r = 0.543; P less than 0.05) for patients with sarcoidosis but not in AH patients. These results suggest that the hyperabsorption of calcium in sarcoidosis is dependent on the serum concentration of 1,25(OH)2D, while in AH it may result from additional vitamin D-independent processes.