Differential Diagnosis for Subacute Cognitive Decline and Parkinsonism

Single Most Likely Diagnosis

• Creutzfeldt-Jakob Disease (CJD): This diagnosis is considered the most likely due to the subacute cognitive decline, generalized weakness, Parkinsonism, and the characteristic MRI findings of T2 hyperintensity in the pons and bilateral thalami without enhancement. The rapid progression over 2 months also supports this diagnosis.

Other Likely Diagnoses

• Progressive Supranuclear Palsy (PSP): Given the Parkinsonism and cognitive decline, PSP is a consideration, although the MRI findings are not as typical for PSP as they are for CJD.
• Multiple System Atrophy (MSA): MSA could explain the Parkinsonism and generalized weakness, but the cognitive decline and specific MRI findings are less characteristic.
• Vascular Parkinsonism: Although less likely given the MRI findings, vascular Parkinsonism could be considered if the patient had a history of vascular disease, but the subacute cognitive decline and specific MRI pattern are not typical.

Do Not Miss Diagnoses

• Wernicke's Encephalopathy: Although the patient's presentation does not classically suggest Wernicke's (which typically includes ophthalmoplegia, ataxia, and confusion), missing this diagnosis could be fatal. It requires immediate treatment with thiamine.
• Toxic or Metabolic Causes: Certain toxins or metabolic derangements (e.g., Wilson's disease, though less likely at this age) could present with similar symptoms and are potentially treatable, making them crucial not to miss.
• Infectious Causes (e.g., Neurosyphilis, Whipple's Disease): These conditions are rare but can present with a wide range of neurological symptoms, including cognitive decline and Parkinsonism, and are treatable with antibiotics.

Rare Diagnoses

• Fatal Insomnia (FI): A rare prion disease that could present with rapid cognitive decline and neurological symptoms, though it typically includes severe insomnia.
• Gerstmann-Sträussler-Scheinker Disease (GSS): Another rare prion disease that presents with cognitive decline and ataxia, but the Parkinsonism and specific MRI findings in this case make it less likely.
• Lewy Body Dementia: While it can present with cognitive decline and Parkinsonism, the subacute progression and specific MRI findings are not as characteristic for Lewy Body Dementia as they are for other diagnoses listed here.