A 55- year- old woman is referred to psychiatric consultation. She has a hx of HIV, contracted from a former sexual partner. She has been prescribed highly active antiretroviral therapy but for years has been only intermittently adherent. Currently, her CD4 count is 200 and her HIV viral load has been escalating. She complains that over the past several months she has been less mentally agile than in the past. She says it takes her significantly longer to rad the newspaper each morning. When she wants to communicate with her daughter, concentrating on writing a text message is difficult and she even finds "my fingers do not cooperate with me when I try to type". Her fine motor skills appear to be worsening. The woman denies any other physical symptoms, such as fever or headache. There are no focal findings on neurological exam. Head compute red tomography (CT), magnetic resonance imaging (MRI), electroencephalography, lumbar puncture, non- HIV viral polymerase chain reaction testing, antibody screens, metabolic parameters including hepatic and renal function, and urine toxicology are all negative. Neurospychological testing shows impairment in information processing speeds, motor skills, and attention. What is the likely diagnosis?

A. Cryptococcal meningitis.
B. Major depressive disorder.
C. Mild neurocognitive disorder due to HIV infection.
D. Vitamins B 12 deficiency.