## 3 Investigations  
On examination, she was alert and orientated. She had not noticed any change in her hearing or sense of smell. There was no evidence of a relative afferent pupillary defect (RAPD). She had a full range of eye movements. There was no facial asymmetry or weakness. Fundoscopy was normal. No evidence of red colour desaturation was detected. She was found to have a right inferior quadrantanopia. There was diminished pinprick and light touch sensation of the right side of face. The remainder of the cranial nerves were intact.  
She had normal tone and reflexes. Power was 5/5 in both the upper and lower limbs. Diminished pinprick and light touch sensation of upper and lower right limbs was present on the right. There were no extrapyramidal or cerebellar signs.  
The patient was hospitalised for further investigation. She initially underwent a computerised tomography (CT) scan of the head, which was reported as normal with no evidence of an intracranial haemorrhage, ischaemic stroke, or a space-occupying lesion.  
Subsequent magnetic resonance imaging (MRI) of the brain and C-spine revealed an area of hyperintense lesion on T2-weighted imaging involving the posterior limb of the internal capsule, adjacent to the left posterior thalamus with perilesional oedema (Figures 1 and 2). Further hyperintensities were noted in the left frontotemporal region. These lesions demonstrated incomplete ring enhancement with gadolinium and facilitated diffusion restriction, consistent with acute demyelinating lesions. The lesions on the scan did not meet the MAGNIMS criteria for a multiple sclerosis diagnosis.  
A lumbar puncture (LP) was performed. Oligoclonal bands were detected in the cerebrospinal fluid (CSF) and serum, with additional bands in the CSF which were not present in the serum. This implied a systemic inflammatory response with an additional CNS only response.  
Full blood count, urea and electrolytes, liver function tests, bone profile, and erythrocyte sedimentation rate were all normal. Syphilis, human immunodeficiency virus (HIV), and hepatitis B and C serologies were negative. The autoimmune profile was normal: \"Anti-AQP-Ab negative, anti-MOG-Ab negative\".  
We also performed a lupus panel: anti-ANA, anti-native DNA, anti-U1 RNP, anti-SnRNP, SSA, SSB, anti-Histone, and anti-phospholipids were all negative.  
An additional antibody panel was performed on CSF and blood serum to indirectly evaluate the haematoencephalic barrier permeability. In particular, measles antibodies showed a CSF/serum ratio of 0.2, not indicative of an intrathecal antibody synthesis. Blood levels were IgG 420 U/mL and IgM 3 U/mL. These values were compatible with the patient-referred puerile infection. Varicella-zoster virus (VZV) antibodies had a CSF/serum ratio of 0.4. The patient has undergone vaccine two years before and she had never developed clinical infection.  
ELISA test did not detect HSV-1 and HSV-2 IgM or IgG in CSF. Since the patient lived near the countryside, we performed an ELISA test for Borrelia burgdorferi, which resulted negative. CXCL13 chemokine on CSF sample was undetectable. Moreover, the patient did not remember any tick bite episode. Finally, we tested SARS-CoV-2 Ab, which was at an undetectable level in CSF, while serum IgG level was high for anti-nucleocapside (anti-N) and anti-spke (anti-S) (IgM negative). These values might be due to the previously executed three-dose COVID vaccine. Solely rubeola antibodies were not analysed. In consideration of the patient's age and work, she had been vaccinated for rubeola, and her last antibody dosage was 37 U/mL four years before.