Frontotemporal Dementia (FTD): This condition is characterized by progressive atrophy of the frontal and/or temporal lobes, leading to significant changes in personality, behavior, and language, along with motor symptoms such as weakness. The frontal parietal atrophy mentioned could be a variant of FTD, particularly the frontotemporal lobar degeneration with motor neuron disease (FTLD-MND), which presents with both cognitive decline and motor symptoms.

Alzheimer's Disease: While primarily associated with temporal lobe atrophy, advanced Alzheimer's can involve the frontal and parietal lobes, leading to a broader range of cognitive and motor symptoms, including weakness.
Vascular Dementia: This condition, resulting from reduced blood flow to the brain, can cause atrophy in various areas, including the frontal and parietal lobes, depending on the location of the vascular damage. It may present with stepwise deterioration and focal neurological signs, including weakness.
Progressive Supranuclear Palsy (PSP): A neurodegenerative disorder that affects movement, control of walking, and balance. It can cause atrophy in the frontal lobe and other areas, leading to significant motor symptoms, including weakness and falls.

Creutzfeldt-Jakob Disease (CJD): A rare, degenerative, fatal brain disorder. It can cause rapid deterioration of mental and motor skills, with symptoms including muscle weakness, and atrophy can be seen on imaging. Given its rapid progression and fatal outcome, it's crucial not to miss this diagnosis.
Prion Diseases: Similar to CJD, other prion diseases can cause rapid neurological decline, including atrophy and weakness. Their rarity and severity make them important not to overlook.
Lyme Disease or Other Infectious Causes: In rare cases, infectious diseases can cause or mimic neurological conditions, including atrophy and weakness. Identifying and treating these conditions early is critical.

Corticobasal Degeneration (CBD): A rare, progressive neurological disorder characterized by atrophy of the cerebral cortex and basal ganglia, leading to motor symptoms such as weakness, rigidity, and dystonia, often asymmetrically.
Huntington's Disease: Primarily known for its impact on the basal ganglia, in rare cases, it can present with significant frontal and parietal involvement, leading to atrophy and a range of motor and cognitive symptoms.
Mitochondrial Disorders: These are a group of conditions that affect the mitochondria, often presenting with neurological symptoms, including weakness and atrophy, due to the high energy demands of the brain.