Otologic manifestations of Susac syndrome

Abstract

Susac syndrome, a rare autoimmune disorder first described as a classic triad (encephalopathy, branch retinal artery occlusion, and sensorineural hearing loss) in 1979 by renowned physician John O. Susac, has been an advancing area of clinical interest and scientific research over the last several decades. This comprehensive review aims to succinctly highlight the breadth and detail of this enigmatic disease, with a primary focus on otologic manifestations. Topics discussed include epidemiology, pathophysiology, clinical manifestations, differential diagnoses, classification schema, laboratory investigations, characteristic audiometric findings, high-yield radiographic imaging, temporal bone histopathology, treatment strategies and overall prognosis.

Keywords: Otology; Sensorineural hearing loss; Susac syndrome; Temporal bone histopathology; Update.

Fig. 1.

Proposed model of pathogenesis for Susac syndrome. Used with permission from E. Bernd Ringelstein. The endothelial cells and basement membrane are oedematous, with loss of vessel wall integrity. As a result, there is subsequent lymphocytic infiltration and thrombotic material accumulation within the vessel lumen. This ultimately results in occlusion of the affected microvasculature (from Kleffner et al., 2012 , mod.).

Fig. 2.

36-year-old female with sensorineural hearing loss in the setting of Susac Syndrome. Pure tone audiometry reveals bilateral asymmetric sensorineural hearing loss, predominantly at the low and middle frequencies. The right ear is graphed with a “○” and the left ear is graphed with an “X”. These responses represent the air conduction results, masked if necessary in both ears. Speech recognition thresholds were 45 decibels in the right ear and 60 decibels in the left ear; word discrimination scores were 96% in the right ear and 88% in the left ear.

Fig 3.

24-year-old female with acute vertigo in the setting of Susac syndrome. Side, left; stimulus, logon; frequency, 500 Hz; number of stimuli, 200; intensity, A 130, B 130, C 120, D 110 dB sound pressure level; masking, off; rate, 4/s; polarity, negative; sensitivity, 10 μV per division; amplitude, A 23.42, B 24.35, C 34.09, D 9.68; latency A 20.8, B 20.8, C 20.8, D 21.6 (from Magliulo et al., 2008 , used with permission from Giuseppe Magliulo).

Fig. 4.

43-year-old female with Susac syndrome characterised by the clinical triad of encephalopathy, branch retinal artery occlusion, and sensorineural hearing loss. T2-weighted midline sagittal imaging reveals mild thinning of the corpus callosum near the junction of the body and the splenium.

Fig. 5.

51-year old female with Susac syndrome and postmortem histopathological findings of the right temporal bone. Used with permission from Chadi Makary. Lower middle turn reveals widespread atrophy and degeneration. The organ of Corti is absent. The tectorial membrane is retracted and partially covered by cells. The spiral limbus reveals patchy atrophy and absent dendrites within the osseous spiral lamina. The stria vascularis is completely atrophic with significant loss of fibrocytes within the spiral ligament (from Francis et al., 2011 , mod.).