Frontotemporal dementia (FTD) defines a group of varied clinical conditions arising from the progressive degeneration of the frontal and temporal lobes of the brain. The three main subtypes of FTD are characterized by the anatomical regions impacted and the corresponding clinical symptoms observed. 

The classic subtypes of FTD are: 

• Behavioral variant FTD (bvFTD): This subtype is characterized by prominent changes in personality, behavior, and social cognition. Patients often display disinhibition, apathy, loss of empathy, compulsive or repetitive actions, and impaired judgment. Executive dysfunction can often affect decision-making and problem-solving skills, severely impacting daily functioning and interpersonal relationships. 

• Nonfluent variant primary progressive aphasia (nfvPPA): This subtype predominantly impacts the frontal lobe, resulting in impaired speech. Clinical symptoms include aphasia, motor speech issues such as apraxia of speech, and reduced speech fluency. Patients may speak in slurred or hesitant speech, and their ability to comprehend complex grammatical structures can be compromised. Over time, language difficulties can worsen, potentially leading to mutism.  

• Semantic variant primary progressive aphasia (svPPA): In this subtype, neurodegeneration primarily affects the temporal lobe, leading to a progressive loss of word meaning. Patients often exhibit fluent speech with marked loss of semantic abilities, including impaired comprehension of word meaning, which can extend to difficulties naming objects or recognizing people. They may maintain fluent motor speech initially, but struggle with understanding and generating meaningful language. 

Each variant presents distinct challenges and clinical manifestations, contributing to the heterogeneity within the FTD spectrum. Early diagnosis and subtype differentiation are crucial for appropriate management and treatment planning, as these conditions can significantly impact patients' quality of life and their ability to interact socially. Advancing our knowledge of dependable neuroimaging biomarkers in FTD can lead to precise and early diagnoses, support suitable disease management strategies, and aid in the evaluation of new treatments during clinical trials of investigational disease-modifying therapeutics.