Abstract
BACKGROUND: Progressive multifocal leukoencephalopathy (PML) is a rare and fatal opportunistic viral demyelinating infectious disease of the central nervous system (CNS). There are various clinical presenting symptoms for the disease. CASE PRESENTATION: This paper presents a clinical case of PML in a patient with B-Chronic lymphocytic leukemia (B-CLL), previously treated with Chlorambucil, later complicated later with COVID-19 and mucormycosis. CONCLUSION: PML can develop in the setting of cellular immune dysfunction. Late diagnosis of this disease based on nonspecific symptoms is common, therefore when we face a neurological complication in a CLL or immunocompromised patient, we should consider PML infection. A remarkable feature of this case is the possible triggering effect of COVID-19 vaccination for emergence of PML as the disease can be asymptomatic or sub-clinical before diagnosis.