Tick-borne encephalitis (TBE) is caused by a virus that belongs to the Flaviviridae family and is transmitted by tick bites. The disease has a biphasic course. Diagnosis is based on laboratory examinations because of non-specific clinical features, which usually entails the detection of specific IgM antibodies in either blood or cerebrospinal fluid that appear in the second phase of the disease. Neurological symptoms, time course of the disease, and imaging findings are multifaceted. During the second phase of the disease, after the onset of neurological symptoms, magnetic resonance imaging (MRI) abnormalities are observed in a limited number of cases. However, imaging features may aid in predicting the prognosis of the disease.

Tick-borne encephalitis (TBE) is a disease caused by a tick-borne encephalitis virus (TBEV) belonging to the Flaviviridae family. The aforementioned virus is transmitted by the bite of infected ticks. In the recent years, TBEV has become a serious public health problem with a steady increase in its incidence, mainly due to the climate changes and spreading the infected ticks into new territories. The standard protocol of TBE diagnosis involves the serological laboratory test with a minor role of imaging techniques such as magnetic resonance imaging. Long-term complications affecting patients daily activities are reported in about 40–50% of the cases. However, no changes are revealed in the laboratory tests or the imaging examination. The development of new imaging techniques such as proton magnetic resonance spectroscopy (¹H-MRS) can broaden the knowledge about TBE, contributing to its prevention. The aim of this study was to assess the usefulness of ¹H-MRS of the brain in patients with TBE. Compared to controls, a statistically significant decrease in the N-acetylaspartate /creatine ratio was found bilaterally in the right and left thalamus as well as a statistically significant increase in the choline/creatine ratio in the right and left thalamus.

With the increased availability of hybrid PET/MRI in recent years, this method is increasingly used for neuroimaging in clinical practice. It combines the advantages of MRI (including high-resolution imaging of intracerebral lesions and data provided from specialised MRI sequences) with the benefits of PET, which visualises functional alterations in the brain, as well as assesses the myelin quantity changes and the severity of inflammation. The use of PET/MRI may help to eliminate the limitations of MRI indicated in imaging demyelinating inflammatory diseases (such as low specificity in imaging demyelination and a weak correlation of findings with clinical symptoms), as well as insufficient sensitivity in detecting lesions present in encephalitis. In addition to supporting the diagnosis of encephalitis, PET/MRI facilitates monitoring of the disease course and assessing the treatment efficacy of inflammatory demyelinating diseases and encephalitis, as well as evaluating the risk of multiple sclerosis relapse. Further multi-centre longitudinal studies are necessary to assess the real clinical potential of PET/MRI among patients with inflammatory demyelination or encephalitis. In addition to MS and AIE, these studies should also include other inflammatory demyelinating diseases (ADEM, NMO, NMOSD, and MOGAD) as well as encephalitis of viral and parasitic aetiology.

With the increased availability of hybrid PET/MRI in recent years, this method is increasingly used for neuroimaging in clinical practice. It combines the advantages of MRI (including high-resolution imaging of intracerebral lesions and data provided from specialised MRI sequences) with the benefits of PET, which visualises functional alterations in the brain, as well as assessing the myelin quantity changes and the severity of inflammation. The use of PET/MRI may help to eliminate the limitations of MRI indicated in imaging demyelinating inflammatory diseases (such as low specificity in imaging demyelination and weak correlation of findings with clinical symptoms), as well as insufficient sensitivity in detecting lesions present in encephalitis. In addition to supporting the diagnosis of encephalitis, PET/MRI facilitates monitoring of the disease course and assessing the treatment efficacy of inflammatory demyelinating diseases and encephalitis, as well as evaluating the risk of multiple sclerosis relapse. Further multi-centre longitudinal studies are necessary to assess the real clinical potential of PET/MRI among patients with inflammatory demyelination or encephalitis. In addition to MS and AIE, these studies should also include other inflammatory demyelinating diseases (ADEM, NMO, NMOSD, and MOGAD) as well as encephalitis of viral and parasitic aetiology.