In this case, the imaging appearances and presence of a pelvic mass are compelling for the diagnosis of paraneoplastic encephalomyelitis. 

CSF

The smear contains scattered lymphocytes, few monocytes and degenerate cells. No malignant cells are identified.

• Lymphocytes 35

• Monocytes 8

• Neutrophils 0

• Eosinophils 0

Antibodies and tumor markers

• CA-125-New 16 U/mL (normal <35)

• CA19.9-New 10 U/ml (normal <37)

• Serum/Plasma CEA-New 2.7 ug/L (normal <5.0)

• ISLET CELL ANTIBODIES - Serum/Plasma GAD (EIA) <0.6 U/mL (normal <5)

• GABA-B Receptor Antibodies: NOT DETECTED

• AMPA Receptor Antibodies: NOT DETECTED

• NMDA Receptor Antibodies: Not Detected

• Anti VGKC Antibody 9 pmol/L (normal <85 )

• Anti-Hu (ANNA-1) antibodies POSITIVE.

Anti-Hu antibodies are detected in paraneoplastic peripheral neuropathy or encephalomyelitis, usually in the setting of small cell lung carcinoma, although many other primaries have been described including the ovary ¹.