History of present illness
A 29-year-old otherwise healthy woman woke up with field loss in her right eye. She denies photopsias, headache, hearing loss, or acute neurological symptoms. She takes a seizure medication but is otherwise healthy.
Ocular examination findings
Her visual acuities were 20/80 in the right eye and 20/20 in the left eye. She had a relative afferent pupillary defect on the right side, and the anterior segment and vitreous were quiet in each eye. The right fundus examination showed three areas of retinal whitening secondary to multiple branch retinal artery occlusions. The left fundus examination was unremarkable.
Imaging
Fundus photographs of the right eye eyeshowed retinal opacification in the superior half of the macula, superior and nasal to the disc; these areas correspond to the distribution of the affected branch retinal arterioles ( Figs. 42.1 and 42.2 ). There is evidence of earlier occlusion of two inferonasal branches with sclerosed segments of the arterioles ( Fig. 42.2 , arrows ). The left eye ( Fig. 42.3 ) was not involved at this time. Fluorescein angiogram (FA) of the right eye ( Fig. 42.4 ) shows multiple occluded arterioles ( Fig. 42.5 ) and the characteristic finding of arteriolar wall staining of the affected and many of the unoccluded arterioles ( Fig. 42.6 ) in contrast to the left eye ( Fig. 42.7 ). Optical coherence tomography shows inner retinal thickening and opacification of the infarcted retina with shadowing of the underlying outer retina ( Figs. 42.8 and 42.9 ).
Questions to ask
- ■
Did the patient have a similar episode or symptoms previously? Clotting disorders, related to factor V Leiden deficiency and protein S or protein C abnormalities, may be associated with recurrent thrombosis. The branch retinal artery occlusions recur in Susac syndrome; hence a history is useful.
- ■
No
- ■
- ■
Does the patient have a history of carotid or cardiovascular disease? Branch retinal artery occlusions can result from carotid atherosclerotic disease, cardiac valvular disease, left atrial myxoma, and patent foramen ovale.
- ■
No
- ■
- ■
Has the patient had any recent cosmetic procedure? Emboli can result from retrograde embolism from triamcinolone injection to a hemangioma on the face or intranasal injections into a turbinate or from retrograde embolism after injection of fillers in cosmetic surgery.
- ■
No
- ■
- ■
Is there hearing loss? The condition, Susac syndrome, affects arterioles in the retina, brain, and inner ear.
- ■
Yes
- ■
- ■
Any previous focal neurological deficits or behavior alterations?
- ■
No
- ■
Branch retinal arterial occlusions, hearing loss, and focal neurological deficits constitute the triad of Susac syndrome. The involvement of the three different structures could be delayed, and a history related to hearing loss or neurological symptoms is useful. The peri–corpus callosal areas and limbic system are involved; hence patients may have “brain fogginess” or bizarre or unexpected behavior changes.
Assessment
This is a case of a 29-year-old woman with recurrent and multiple simultaneous branch retinal artery occlusions with typical fluorescein staining of the affected and some unaffected arterioles. Though she did not have hearing loss or neurological symptoms at the time of presentation, she had peri–corpus callosal infarcts on magnetic resonance imaging (MRI), confirming the clinical diagnosis of Susac syndrome.
Differential diagnosis
Branch retinal artery occlusions from other causes should be considered.
- ■
Bartonella henselae retinitis (cat scratch disease) at the site of a retinal arteriole: neuroretinitis and/or patches of focal white retinitis are typically seen; these are not present in our patient; also no history of owning cats in this patient
- ■
Toxoplasma retinitis in the vicinity of a retinal arteriole causing occlusion: no areas of retinitis or vitritis in this patient
- ■
Protein S or protein C deficiency: protein C and protein S levels not checked as the patient had the typical fluorescein pattern of fusiform arteriolar wall staining that is unique to Susac syndrome and does not warrant testing for other conditions
- ■
Fat embolism in a patient with persistent foramen ovale: typically posttraumatic or postpartum
- ■
Talc embolism from intravenous drug use in patient with patent foramen ovale: usually multiple crystalline deposits seen in the retina and arteriolar lumen
- ■
Embolism from a carotid plaque: refractile embolus if cholesterol embolus
- ■
Embolism from a left atrial appendage or valvular vegetations: no work-up done to rule out calcific plaques or platelet fibrin emboli as the FA was diagnostic of Susac syndrome
- ■
Retrograde embolism from triamcinolone injection to a hemangioma on the face or intranasal injections into a turbinate
- ■
Retrograde embolism from injection of fillers in cosmetic surgery
- ■
Branch retinal artery occlusion in a prepapillary loop
- ■
Sickle cell retinopathy with arteriolar occlusion
- ■
Systemic lupus erythematosus (SLE) and, rarely, dermatomyositis
Diagnosis
Susac syndrome (recurrent idiopathic branch retinal artery occlusions)
Multimodal imaging
- ■
Fundus photographs
- ■
Multiple areas of retinal whitening in the right eye result from branch retinal artery occlusions. There are almost never any retinal hemorrhages in Susac syndrome, unlike SLE and dermatomyositis.
- ■
- ■
FA
- ■
The appearance on FA of fusiform staining of the affected arterioles and often many of the non-occluded arterioles is a pathognomonic sign in Susac syndrome. Eyes with Bartonella or toxoplasma retinitis will show staining of the patch of retinitis in the vicinity of the occluded vessel. An embolus causes occlusion at a bifurcation; however, the occlusion in Susac syndrome is not at a bifurcation, but along a segment of the arteriole. A careful examination of the fundus will reveal emboli, retinitis, periarteriolar plaques, or features of sickle cell retinopathy. Lupus retinopathy and dermatomyositis result in several retinal hemorrhages and the fluorescein leakage is widespread, unlike the isolated fusiform staining of the arteriolar wall in Susac syndrome.
- ■
- ■
MRI
- ■
MRI of the brain, especially sagittal sections to look for peri–corpus callosal white matter changes, helps corroborate the diagnosis.
- ■
- ■
Audiogram
- ■
An audiogram to look for sensory neural hearing loss may be done.
- ■
- ■
Lab tests
- ■
They are not necessary to rule out other causes such as protein C and protein S deficiencies if the typical FA pattern is seen. However, if the affected arteriole is completely occluded preventing the fluorescein from passing beyond the occlusion, and no other arteriole is partly involved, the typical fusiform staining of the arteriole is not seen. Lab tests to rule out protein C and protein S deficiency will be necessary in that situation.
- ■
Management
- ■
High-dose systemic steroids tapered over 6 to 8 weeks
- ■
Intravenous immunoglobulin (IVIG)
- ■
Immunomodulatory drugs such as mycophenolate mofetil
- ■
Rituximab
Follow-up care
- ■
Regular follow-up to see if the lesions recur and wide-field FA imaging to monitor for resolution and disappearance of the arteriolar wall staining and leakage.
- ■
Annual Goldmann visual field to look for asymptomatic field loss.
- ■
Maintenance immunosuppression with mycophenolate mofetil or other immunosuppressives.
Key points
- ■
Consider Susac syndrome in patients with recurrent and multiple branch retinal artery occlusions with hearing loss and/or neurological changes.
- ■
Sometimes the triad of vision loss, hearing loss, and neurological features can manifest over several years.
- ■
Susac syndrome patients need urgent neurologic evaluation with MRI imaging to look for peri–corpus callosal changes on T2 fluid-attenuated inversion recovery sequences.
- ■
IVIG, high-dose systemic steroids, and immunosuppressive medications are urgently needed.
- ■
Neurology, otolaryngology, and retinal follow-up is needed on a regular basis.
- ■
There is no definitive blood test available to confirm circulating antibodies or other biomarkers.
Algorithm 42.1 : Algorithm for differential diagnosis for susac syndrome
