Case report: Anti Yo encephalitis - psychiatric presentation

Introduction: Autoimmune encephalitis (AE) comprises a group of non-infectious immune-mediated inflammatory disorders of the brain parenchyma often involving the cortical or deep grey matter with or without involvement of the white matter, meninges or the spinal cord. Anti Yo encephalitis is a rare condition where anti Yo antibodies cause brain inflammation. Symptoms usually relate to neurological disorders, mainly ataxia, gait instability and dysarthria. It is usually seen as a part of a paraneoplastic syndrome related to ovarian and breast cancer, but not in every case. It is a rare condition, not very often seen in minors and no rare case reports on these condition is seen in literature.

Case presentation: Our patient is a 17-year old male, who presented to family medicine doctor with symptoms of fever and signs of viral infection. A day after a sudden change in the mental state has been observed with cognitive impairment, delusional interpretation, changes in personality, as well with lesion of short term memory. On the neurological side, sudden onset of headache and instability of walking has been observed. During the course, meningeal signs become positive and gait problems became more pronounced, so an admission to the neuropediatric ward was initiated. A psychiatric consult has been realized because of additional symptoms of agressiveness and intensive delusions, auditory hallucinations and insomnia. Atypical antipsychotics have been intiated starting with low doses, up to 10 mg of olanzapine. The patient has been diagnostically evaluated with laboratory findings with no specific results, ultrasonography of the abdomen, urinary system and testicles with no valuable findings, CT of the abdomen and pelvis- no pathological finding, EEG - non specific findings but with general slowing, brain MRI scan with T2/FLAIR hyperintensities in the white matter, and subacute cerebellar degeneration and lumbal puncture - which finding revealed low positive results for anti Yo encephalitis in the cerebrospinal fluid and blood. Due to progressive worsening of the neurological and mental state, high doses of corticosteroids, despite the risk of mental state worsening have been initiated, but with everyday psychiatric check-up. High doses of corticosteroids together with antipsychotics resulted in improvement of the neuropsychological state after a few days. No need for rise of dose of antipsychotics was needed. Stepwise discontinuation of both medications with detailed examination by neuropediatrican and psychiatrist resulted with no worsen of symptoms.

Conclusion:: Multidisciplinary approach is key the to success in rare cases diagnose and treatment where risk benefit evaluation plays a key role. Psychiatric symptoms with an sudden and abrupt onset should be evaluated for other causes primarily focused on the brain but other organ systems, as well. Proper and timely diagnosis is the key to remission of symptoms.

Keyword: autoimmune encephalitis, anti YO encephalitis, psychiatric symptoms

References

1. Aslan, E., Varoglu, A. O., Baysal, B., & Tatoglu, M. T. (2026). A Rare Case of Anti-Yo Positive Paraneoplastic Limbic Encephalitis Associated with Thyroid–Parathyroid Adenoma. The Cerebellum, 25(1), 12.
2. Tosunoglu, B., Güneş, H., Kina, H., & Çokal, B. (2024). Anti-Yo antibody-associated Autoimmune Encephalitis due to Breast Adenocarcinoma in a male patient. Fortschritte der Neurologie· Psychiatrie, 92(10), 423-425.
3. Aytaç A, Kasapoglu H, Yanık Keyik B. Anti-Yo positive paraneoplastic limbic encephalitis associated with nasopharyngeal carcinoma: A rare case. Radiol Case Rep. 2025 Nov 15;21(2):593-598.
4. Bost C, Pascual O, Honnorat J. Autoimmune encephalitis in psychiatric institutions: current perspectives. Neuropsychiatr Dis Treat. 2016 Oct 27;12:2775-2787
5. Abboud, H., Probasco, J. C., Irani, S., Ances, B., Benavides, D. R., Bradshaw, M., … & Autoimmune Encephalitis Alliance Clinicians Network. (2021). Autoimmune encephalitis: proposed best practice recommendations for diagnosis and acute management. Journal of Neurology, Neurosurgery & Psychiatry, 92(7), 757-768.