Anti-kelchlike protein 11 antibody-associated encephalitis: Two case reports and review of the literature.

BACKGROUND AND PURPOSE: Kelchlike protein 11 antibodies (KLHL11-IgGs) were first described in 2019 as a marker of paraneoplastic neurological syndromes (PNSs). They have mostly been associated with testicular germ cell tumors (tGCTs). METHODS: Two patients with KLHL11-IgG encephalitis are reported, and the literature is comprehensively reviewed. RESULTS: Patient 1 had been in remission from a tGCT 10 years prior. He developed episodic vertigo and diplopia progressing over a few days. Treatment with corticosteroids (CSs) was started a few days after symptom onset. Patient 2 had transient diplopia, which resolved spontaneously. Visual problems persisted for 7 months, when he additionally developed a progressive cerebellar syndrome. One year after onset, CS treatment was started. Initial magnetic resonance imaging was unremarkable in both patients, but analysis of cerebrospinal fluid (CSF) revealed chronic inflammation. KLHL11-IgG was positive in both patients (Patient 1 only in CSF, Patient 2 in serum). Neoplastic screening has so far not revealed any signs of active underlying malignancy. We found 15 publications of 112 patients in total with KLHL11-IgG encephalitis. Most patients (n = 82) had a cerebellar syndrome with or without signs of rhombencephalitis. The most common symptoms were ataxia (n = 82) and vertigo (n = 47), followed by oculomotor disturbances (n = 35) and hearing disorders (n = 31). Eighty of 84 patients had a GCT as an underlying tumor. CONCLUSIONS: Our cases demonstrate classical symptoms of KLHL11-IgG encephalitis. Early diagnosis and therapy are imperative. As with other PNSs, clinical awareness is needed and further studies are required especially in regard to therapeutic management.