Ocular toxoplasmosis in HIV patients — MRI findings

Clinical History

The patient presented sudden unilateral optical impairment of the left eye that lasted 3 days without signs of infection. He was not receiving antiretroviral therapy.
Toxo IgM, Toxo IgG were positive, whereas CMV, EBV, Leptospira, Borrelia, RPR, HSV, VZV antibodies, SACE, Mantoux were negative. Vitreous PCR was not submitted due to the patient’s refusal.

Imaging Findings

CT of the abdomen and thorax didn’t reveal any abnormalities, thus the presence of lymphoma or sarcoidosis was excluded.
He was submitted on MRI of the orbits with T1 with and without fat-suppressed pre and post gadolinium images, T2 TSE and T2 fat sat weighted images in axial, sagittal and coronal planes. The MRI revealed swelling of the left optic nerve with a maximum sagittal diameter of 7 mm (Fig. 1) and contrast enhancement of the nerve sheath, findings compatible with inflammation (Fig. 2, 3). There was also presented impingement on the sclera, retina and choroid (Fig. 1, 2). The inflammatory changes were extending to the adjacent periorbital fat tissue (Fig. 2). The patient was also submitted on brain MRI which didn’t show pathologic findings. The new MRI two months after the initiation of treatment illustrated improvement without swelling and contrast enhancement of the left optic nerve and an almost normal diameter (Fig. 4, 5).

Discussion

Toxoplasmosis is caused by Toxoplasma gondii which is found worldwide. It is an intracellular parasite that infects birds and mammals. Its specific host is the cat and other felidae species. It is transmitted to humans primarily by ingestion of cysts in half-cooked pork or lamb or contaminated vegetables [1].
Toxoplasmosis most commonly is presented during childhood but can be acquired at any age as well. Most of the infections are asymptomatic and the percentage of antitoxoplasma IgG ranges from 15-20% in Northern Europe to 80% or more in parts of the developing world [2].
In contrast to its presentations in immunocompetent individuals, toxoplasmosis in HIV-infected patients is a fulminant disease and a main cause of CNS mordibity and mortality [3]. Ocular and orbital disease is less common than cerebral disease, however, it may be the first manifestation of life-threatening systemic toxoplasmosis in HIV-infected patients [3, 4].
Ocular toxoplasmosis is mostly characterized by multifocal sites of retinochoroidal infection with less accompanying vitritis, vasculitis and haemorrhage. A pre-existing retinochoroidal scar is rarely present, as a result of newly acquired disease. Bilateral eye involvement also may be seen and proliferative vitreoretinopathy may accompany later stages of the disorder [2, 5].
Serologic studies have been relatively unaccurate for the diagnosis of toxoplasmosis in HIV-infected patients. However, toxoplasmosis is unlikely in a patient with a negative IgG anti-Toxoplasma antibody [5].
Fundoscopy may reveal swelling of the optic disc, macular oedema, and retinal haemorrhages [6].
MRI of the orbits may illustrate neuritis, retinochoroiditis, and/or multiple enhancing lesions in the brain which are essential for the diagnosis of ocular and/or cerebral toxoplasmosis [6]. The orbits protocol should contain T1SE and TSE with and without fat suppressed images pre and post gadolinium as well as T2 and T2 fat sat at least in two planes. The combination of fat and fluid suppression is crucial for imaging the optic nerve, solving the problem of orbital fat and the surrounding T2 hyperintensity of CSF within the optic nerve sheath [7].

Differential Diagnosis List

Final Diagnosis

Laboratory tests and MRI confirmed toxoplasmosis of the optic nerve.

URL:	https://www.eurorad.org/case/13761
DOI:	10.1594/EURORAD/CASE.13761
ISSN:	1563-4086