Tuesday, November 22, 2016

MOC Exam Topic: Acute Hemorrhagic Leukoencephalopathy

First recognized as a discrete entity by Weston Hurst in 1941, acute hemorrhagic leukoencephalopathy (AHL) is a usually fatal disease characterized clinically by an abrupt onset of fever, neck stiffness, and neurological deficits, often progressing rapidly to seizures and coma. The presenting clinical picture is similar to that of acute disseminated encephalomyelitis (ADEM) but with a more fulminant course. At autopsy, the brain is swollen with multiple petechial hemorrhages centered in the white matter. Large foci of necrosis with cavitation may be present. The cerebral cortex and basal ganglia usually appear intact. Histologically, perivascular demyelinating lesions consist of ball or ring hemorrhages surrounding necrotic venules. There are cuffs of mononuclear cells and neutrophils. There is also substantial axonal injury in the affected areas. The lesions are indistinguishable from ADEM, but the extent of microvascular damage and therefore hemorrhage is is greater. An allergic mechanism is postulated.

FIGURE 3. A (H&E, 100×), B (LFB/PAS, 100×), and C (HAM-56 IHC, 400×). Light microscopic studies revealed thin sleeves of pallor surrounding small-caliber parenchymal blood vessels (A) which correspond to areas of demyelination on special stain (B). Macrophages stain strongly positive for macrophage marker HAM-56 (C). From Lann MA, et al.  2010 Mar;31(1):7-11.

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