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Malaria is a common cause of death in certain tropical countries, with sub-Saharan African children under 5 years old representing the vast majority of fatalities each year. Cerebral malaria, defined as an unarousable coma in a malaria-infected patient with no apparent alternative explanation for altered mental status, is a severe and often fatal complication of malaria. Patients with cerebral malaria or other forms of severe malarial infection commonly develop a classic pattern of retinal changes first described in Malawian children in 1993.
The pathogenesis of malarial retinopathy is associated with that of cerebral malaria, i.e. sequestration of infected red blood cells in retinal and cerebral microvasculature, causing vessel obstruction and reduced blood flow resulting in downstream ischemia and hypoxia. Dysregulation of the angiopoietin-Tie-2 pathway, an important regulator of endothelial cell function and vessel integrity, has been linked with both retinopathy and mortality in pediatric cerebral malaria. Cerebral malaria and malarial retinopathy are most commonly seen in severe infections by Plasmodium falciparum, though patients infected with Plasmodium vivax have also been noted to have some features of malarial retinopathy.
The characteristic changes of malarial retinopathy consist of retinal whitening, vessel discoloration, retinal hemorrhages, and optic disc edema. Fundus findings are typically symmetrical between the two eyes.
Retinal whitening may be seen in the macula (sparing the foveola), though some patients may only develop retinal whitening in the periphery. Hence, indirect ophthalmoscopy through a dilated pupil is important for establishing the diagnosis. While some patients with malaria have been noted to have cotton-wool spots, the whitening typical of malarial retinopathy tends to be less vivid, more widely distributed, and may be poorly demarcated. Fluorescein angiography studies have demonstrated that this whitening corresponds to retinal non-perfusion. Patients with cerebral malaria commonly develop thrombi composed of fibrin and platelets, and it is thought that thrombosis of retinal microvasculature induces ischemia and subsequent hypoxia, leading to intra-cellular edema and loss of retinal transparency.
Retinal vessels may be noted to be orange or white, particularly in the retinal periphery; and tramlining may be seen in larger vessels. Discoloration may be noted in discrete sections of vessels or in a branching pattern. To date, this finding has only been described in the pediatric population. The discoloration is likely related to drastically reduced hemoglobin levels in parasitized red blood cells that tend to sequester in retinal capillaries and in branch points of the peripheral retinal vasculature.
Intra-retinal hemorrhages, often with a white center and resembling Roth spots, are a common finding in patients infected with malaria. While patients with asymptomatic or mild infections may have no or few hemorrhages, patients with severe malaria may manifest hemorrhages that are too numerous to count. Hemorrhages may sometimes involve all layers of the retina, extending into both the pre-retinal and sub-retinal space.
Optic disc edema
Optic disc edema can be seen in various etiologies of coma, including cerebral malaria. While this sign is not specific to malarial retinopathy, its presence in patients with cerebral malaria is a particularly poor prognostic sign.
Additional clinical signs in cerebral malaria
Diagnosing coma caused by cerebral malaria versus other causes of encephalopathy is a challenge in resource-poor areas, and misdiagnosis can have life-threatening consequences. For example, a prospective autopsy study in Malawi found that 23% of children who died with the diagnosis of cerebral malaria actually did not have the histopathological hallmarks of cerebral malaria, but had other causes of death. Misdiagnosis occurs because the clinical manifestations of severe malaria in children (coma, seizures, hypertonia, hyperventilation, and anemia) are not specific to malaria. When children present with these symptoms, along with malaria parasites in the peripheral blood, a presumptive diagnosis of cerebral malaria is often made, yet the parasitemia may be an incidental finding in endemic regions. In much of these same regions, laboratory and radiographic investigations to narrow the differential are typically not available.
The unique retinal findings in cerebral malaria correlate to the histopathology and severity of the disease. These are the most specific and sensitive signs of cerebral malaria that are available. One study showed that the detection of malarial retinopathy in comatose children with malarial parasitemia had a positive predictive value of 95% and a negative predictive value of 90% for the diagnosis of cerebral malaria, compared to a positive predictive value of only 77% in patients diagnosed clinically, using World Health Organization criteria, without a dilated funduscopic exam. Current research focuses on the utility of non-ophthalmologists to directly examine and/or capture retinal images for automated and expert review. Access and education around these new developments, as well as to equipment, supplies, and training, remain a challenge.
Though trauma may be associated with retinal whitening, hemorrhages, and optic disc edema, trauma is not known to cause white or orange discoloration of retinal vasculature.
Treatment requires systemic anti-malarial therapy guided by local anti-malarial sensitivity and resistance patterns. No treatment for the retinopathy itself has been described thus far.
The majority of children with cerebral malaria regain consciousness within 48 hours without any permanent neurological sequalae, while approximately 10% will develop lasting neurological deficits and about 20% will die from the illness. The severity of malarial retinopathy in these children is correlated with longevity of coma and increased risk of death, with the presence of optic disc edema and peripheral retinal whitening conferring the highest relative risk. Studies in adults infected with Plasmodium falciparum found that mild retinopathy may be present in adults with uncomplicated malaria, but that more severe malarial retinopathy was associated with more severe systemic disease.
In pediatric survivors of severe malaria, retinopathy resolves within 1-4 weeks. While some patients may develop cortical blindness as a neurological complication of severe malaria, children who survive severe malaria have not been found to have long-term visual deficits attributable to their retinal changes. No published data are available regarding long-term visual outcomes in adults.
- World Health Organization. World Malaria Report 2019. https://www.who.int/publications-detail/world-malaria-report-2019. Published December 4, 2019. Accessed April 4, 2019.
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