A 33-year-old woman at 32 weeks gestational age presented with a 4-week history of encephalopathy and hearing loss. Her past medical history was unremarkable, and she was only taking prenatal vitamins. The neurological examination was remarkable for cognitive slowing, apathy and difficulty hearing bilaterally. Brain MRI revealed bilateral caudate nuclei, lentiform nuclei, external capsules and corpus callosum FLAIR hyperintensities (Figure 1a). Audiological testing confirmed bilateral sensorineural hearing loss. Ophthalmological examination showed visual acuity of 20/20 bilaterally. Humphrey visual field analyzer testing was normal. Fundus fluorescein angiography to assess for branch retinal artery occlusion (BRAO) was not performed because of its relative contraindication in pregnancy. ^{Reference Kornblau and El-Annan1} A lumbar puncture did not show evidence of any infectious, inflammatory or autoimmune process.

Figure 1. Brain MRI depicting basal ganglia and corpus callosum involvement in Susac syndrome. (A) Axial and sagittal brain MRI with T2 FLAIR depicting hyperintense signal in the bilateral basal ganglia and corpus callosum. (B) Axial and sagittal brain MRI with T2 FLAIR showing improvement in signal abnormality in the basal ganglia and corpus callosum four months post- treatment initiation.

The patient was acutely treated with IVIG 2 g/kg over 5 days and high-dose steroids of 1 g methylprednisolone IV once daily for 3 days. This was followed by monthly IVIG and 50 mg prednisone maintenance therapy with a slow taper over a few months. At a 4-month follow-up, she endorsed improvement in cognition and hearing loss. Repeat audiological testing revealed near resolution of sensorineural hearing loss in the right ear, but ongoing profound hearing loss in the left ear. In addition, she had a successful at-term delivery without any fetal or neonate complications and has continued to show disease stability at one year.

Repeat MRI 4 months after initial imaging showed resolution of basal ganglia FLAIR hyperintensities and near resolution of other brain lesions including the corpus callosum (Figure 1b).

Susac syndrome is a rare autoimmune vasculo-occlusive disease in which circulating antibodies attack the vascular endothelium, resulting in arterial microinfarcts affecting the inner ear, retina and CNS. ^{Reference Dorr, Krautwald and Wildemann2,Reference Pereira, Vieira, Maio, Moreira and Sampaio3} Diagnosis is based on clinical presentation, brain MRI, audiometry and retinal fluorescein angiography. Although the classic triad of Susac syndrome includes encephalopathy, hearing loss and BRAO, ^{Reference Kleffner, Duning and Lohmann4,Reference Kleffner, Dörr and Ringelstein5} only 13% of patients exhibit all three at disease onset. ^{Reference Dorr, Krautwald and Wildemann2} Other potential diagnoses include MS, ADEM, CNS vasculitis, hypoxic ischemic encephalopathy and cerebrovascular disease.

MRI findings include multiple hyperintense foci on T2-weighted imaging involving both the white and gray matter, corpus callosum, leptomeninges, thalamus and cerebellum. ^{Reference Susac, Murtagh and Egan6} Involvement of the corpus callosum with characteristic “snowball” lesions is a pathognomonic finding on MRI. ^{Reference Susac, Murtagh and Egan6} Epidemiologically, the disease mainly affects young women with a female/male ratio of 3:1. ^{Reference Pereira, Vieira, Maio, Moreira and Sampaio3}

Several case reports indicate that pregnancy or the postpartum period may exacerbate Susac syndrome, suggesting that immune modulation during pregnancy affects this autoimmune condition. ^{Reference Ioannides, Airey, Fagermo, Blum, McCombe and Henderson7} To date, there are 33 cases of Susac’s in pregnancy, the majority of which describe several corpus callosum lesions, with 4 cases showing additional basal ganglia involvement. Of these four cases, two patients presented in the antenatal period with either persistent or partial remission of symptoms despite therapies. ^{Reference Willekens and Kleffner8}

To our knowledge, this is the first report of Susac syndrome in the antenatal period with predominant basal ganglia involvement, showing near-complete imaging resolution posttreatment, successful term delivery and improved cognitive symptoms and hearing. Furthermore, our case emphasizes the benefits of timely diagnosis and early aggressive therapy in Susac syndrome.