Frontotemporal Dementia (FTD): This is a group of brain disorders caused by cell degeneration in the brain's frontal and temporal lobes. A normal amyloid PET scan supports this diagnosis since FTD is not associated with amyloid deposition. FTD can present with a range of symptoms including changes in personality, behavior, and language, which can mimic or be indistinguishable from other forms of dementia in early stages.

Vascular Dementia: Caused by reduced blood flow to the brain, often as a series of small strokes or changes in the brain's blood vessels. A normal amyloid PET scan does not rule out vascular dementia, as the pathology is related to vascular changes rather than amyloid plaques.
Lewy Body Dementia (LBD): Characterized by the presence of Lewy bodies in the brain, which are abnormal protein clumps. While some patients with LBD may have amyloid deposition, a significant portion may have normal amyloid PET scans, making LBD a consideration in dementia with normal amyloid imaging.
Mixed Dementia: Some patients may have a combination of different dementia pathologies, including Alzheimer's disease, vascular dementia, and others. Even if the amyloid PET is normal, suggesting minimal or no Alzheimer's disease pathology, mixed dementia could still be a consideration if other pathologies are present.

Creutzfeldt-Jakob Disease (CJD): A rare, degenerative, fatal brain disorder. It's crucial to consider CJD because it is rapidly progressive and has a distinct clinical presentation that can sometimes mimic other dementias. Early diagnosis is critical for management and to prevent transmission, although a cure is not available.
Normal Pressure Hydrocephalus (NPH): Characterized by the buildup of cerebrospinal fluid in the brain's ventricles, leading to increased pressure. NPH can cause dementia, gait disturbance, and urinary incontinence. It is treatable with the placement of a shunt, making it a critical diagnosis not to miss.
Reversible Causes of Dementia: Such as vitamin B12 deficiency, hypothyroidism, or chronic infections. These conditions can cause or mimic dementia symptoms and are crucial to identify because they are potentially reversible with appropriate treatment.

Prion Diseases (other than CJD): Such as fatal familial insomnia or Gerstmann-Sträussler-Scheinker disease. These are rare, genetic disorders that affect the brain and are characterized by the accumulation of abnormal prion protein.
Huntington's Disease: An inherited disorder that causes progressive damage to the brain, particularly areas involved in movement control and cognition. While primarily known for its motor symptoms, cognitive decline and dementia are significant components of the disease.
Inherited Forms of FTD: Such as those caused by mutations in the GRN, C9ORF72, or MAPT genes. These are less common than sporadic FTD but are important to consider, especially in patients with a strong family history of dementia.