Rituximab-induced progressive multifocal leucoencephalopathy (PML) in a patient treated for idiopathic thrombocytopenic purpura
Presentation
Few months history of headaches with Cerebellar syndrome in a patient treated with rituximab (immunosuppressive monoclonal antibody therapy) and steroids for idiopathic thrombocytopenic purpura since the age of 1 and 1/2 year.
Patient Data
There is an ill-defined left temporal mass around the temporal horn isodense to the cortical grey matter with a large surrounding low attenuation area and mass effect on the midline structures with dilatation of the contralateral lateral ventricle. A low attenuation area is also noted in the left cerebellum.
The MRI exam was performed immediately after the CT scan and demonstrates:
- left temporal lesion with irregular margin measuring 36 x 32 x 30 mm of low signal on T1 centrally and isosignal to the cortical grey matter peripherally and iso-to slightly high signal on FLAIR and T2 with vivid enhancement on postcontrast sequences and peripheral restricted diffusion on DWI/ADC. Extensive surrounding FLAIR and T2 high signal with no restricted diffusion extending to the subcortical U-fibers. A mass effect is noted on the midline structures. Increased rCBV values in the peripheral region of the lesion. The MRS shows significant increase in choline and reduced NAA and lactate
- left cerebellar lesion measuring 16 x 12 x 9 mm, isointense to the cortical grey matter on T1 and FLAIR, slightly high signal on T2 with vivid enhancement on postcontrast sequences with no restricted diffusion. Surrounding FLAIR and T2 high signal is also noted
Follow-up MRI performed two months after high-dose glucocorticoid therapy shows a significant improvement with decrease in size of the temporal lesion with almost complete regression of the left cerebellar lesion.
Case Discussion
The history of long-term rituximab treatment, the MRI features and significant clinical/imaging improvement under high-dose glucocorticoid therapy are suggestive of a rituximab-induced progressive multifocal leucoencephalopathy (PML). The main differential diagnosis in such a case is CNS lymphoma.
Rituximab is an immunosuppressive monoclonal anti-CD20 used in several diseases such as diffuse large B-cell NHL, rheumatoid arthritis, chronic lymphocytic leukemia, Wegener granulomatosis 1,2 and recently as the second-line treatment of refractory/relapsing thrombotic thrombocytopenic purpura 3,4. The rituximab-induced PML has an incidence around 1 of 30,000 cases 1.