Retinal pathology of pediatric cerebral malaria in Malawi

Abstract

Introduction: The causes of coma and death in cerebral malaria remain unknown. Malarial retinopathy has been identified as an important clinical sign in the diagnosis and prognosis of cerebral malaria. As part of a larger autopsy study to determine causes of death in children with coma presenting to hospital in Blantyre, Malawi, who were fully evaluated clinically prior to death, we examined the histopathology of eyes of patients who died and underwent autopsy.

Methodology/principal findings: Children with coma were admitted to the pediatric research ward, classified according to clinical definitions as having cerebral malaria or another cause of coma, evaluated and treated. The eyes were examined by direct and indirect ophthalmoscopy. If a child died and permission was given, a standardized autopsy was carried out. The patient was then assigned an actual cause of death according to the autopsy findings. The eyes were examined pathologically for hemorrhages, cystoid macular edema, parasite sequestration and thrombi. They were stained immunohistochemically for fibrin and CD61 to identify the components of thrombi, beta-amyloid precursor protein to detect axonal damage, for fibrinogen to identify vascular leakage and for glial fibrillary acidic protein to detect gliosis. Sixty-four eyes from 64 patients were examined: 35 with cerebral malaria and 29 with comas of other causes. Cerebral malaria was distinguished by sequestration of parasitized erythrocytes, the presence and severity of retinal hemorrhages, the presence of cystoid macular edema, the occurrence and number of fibrin-platelet thrombi, the presence and amount of axonal damage and vascular leakage.

Conclusions/significance: We found significant differences in retinal histopathology between patients who died of cerebral malaria and those with other diagnoses. These histopathological findings offer insights into the etiology of malarial retinopathy and provide a pathological basis for recently described retinal capillary non-perfusion in children with malarial retinopathy. Because of the similarities between the retina and the brain it also suggests mechanisms that may contribute to coma and death in cerebral malaria.

Figure 1. Fundus photograph displaying malarial retinopathy consisting of multiple white centered hemorrhages, macular whitening (arrowheads) and orange discoloration of vessels (arrow).

Figure 2. Photomicrograph of retinal vessels showing sequestration of parasitized red blood cells containing late stage parasites.

Figure 3

A. Representative gross photo of malarial retinopathy showing multiple white-centered hemorrhages. B. Low power photomicrograph of hemorrhages involving all layers of the retina, including beneath the internal limiting membrane as well as subretinal hemorrhage with shallow detachment.

Figure 4. Photomicrograph of cystoid macular edema in the outer plexiform layer (arrows).

Figure 5

A. Photomicrograph of retinal hemorrhage with a central vessel containing a thrombus sectioned obliquely (arrow). B. Thrombus in a larger vessel without surrounding hemorrhage. Note that some of the surrounding capillary-sized vessels contain thrombi (arrows) while others do not (arrowhead). C&D. Immunohistochemical staining for fibrin (C), and CD61 to identify platelets (D). (C: Anti-fibrin, hematoxylin counterstain; D: Anti-CD61, hematoxylin counterstain.)

Figure 6. Photomicrograph of immunohistochemical staining for β-APP in nerve fiber layer.

(Anti-β-APP, hematoxylin counterstain.)

Figure 7. Photomicrograph of immunohistochemical staining for fibrinogen surrounding a small vessel (arrowhead) and in the spaces of cystoid macular edema (arrow).

(Anti-fibrinogen, hematoxylin counterstain.)

Figure 8. Photomicrograph of immunohistochemical staining for glial fibrillary acidic protein in retinal Muller cells.

(Anti-GFAP, hematoxylin counterstain.)