To report a patient with Kelch-like protein-11 antibody related encephalitis associated with spontaneously regressed testicular germ cell tumor.

We present a 45-year-old male with nine-year history of progressive cerebellar atrophy of unclear etiology associated with ataxia, dysmetria, dysarthria, diplopia, and nystagmus, who was admitted for subacute neuropsychiatric/cognitive impairment. Symptoms included auditory and tactile hallucinations, severe paranoia, and recurrent panic attacks. Brain MRI demonstrated nonenhancing left temporal lobe T2/FLAIR hyperintensities. EEG captured frequent left hemispheric electrographic seizures originating in the posterior temporal lobe. CSF analysis showed pleocytosis and elevated protein. Infectious workup was negative, but autoimmune/paraneoplastic workup returned positive for KLHL11 antibody. 

Treatment included two courses of methylprednisolone and IVIG, five sessions of plasmapheresis, and antiseizure medication titration over repeated hospitalizations for breakthrough seizures, lethargy, and worsening ataxia and dysarthria. The patient ultimately underwent left radical orchiectomy after ultrasound identified a hypoechoic lesion in the left testicle. Histology was suspicious for regressed TGCT given fibrotic scarring, atrophic seminiferous tubules, and microlithiasis. Subsequent total body FDG PET/CT did not identify active malignancy. After orchiectomy, the patient began monthly cyclophosphamide. Thus far, neuropsychiatric symptoms have resolved, cognition has moderately improved, and cerebellar symptoms have stabilized.

This case illustrates that KLHL11 encephalitis should be suspected in male patients with symptoms associated with subacute to chronic onset cerebellar atrophy, hearing loss, brainstem pathology, as well as limbic encephalitis. This case also highlights that detailed investigations for malignancy, including testicular cancer, should be sought for a better outcome.