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PubMed This is a summary of 15 peer-reviewed journal articles Updated
Neurology · Behavioral Variant Frontotemporal Dementia

Imaging and Biomarkers

At a Glance

Diagnosing behavioral variant frontotemporal dementia (bvFTD) requires imaging and biomarker tests to identify physical brain changes. Doctors use MRI and PET scans to find brain shrinkage or low energy use, and the NfL blood test to confirm brain cell death, distinguishing bvFTD from mental illness.

Confirming a diagnosis of behavioral variant frontotemporal dementia (bvFTD) requires more than just observing behavior; it requires looking for physical evidence of brain change. Because the early symptoms closely mimic psychiatric conditions like depression or bipolar disorder, doctors use a combination of advanced imaging and biological markers (biomarkers) to “see” the disease [1][2].

Looking for “Shrinkage”: The Structural MRI

A structural MRI is often the first step. The doctor is looking for atrophy—the physical shrinking of brain tissue as cells die off.

  • Key Areas: In bvFTD, atrophy typically appears in the frontal lobes (behind the forehead) and the temporal lobes (near the ears) [3][4]. Specifically, shrinkage in the frontoinsular and mesial temporal regions is a hallmark of the disease [5].
  • Asymmetry: It is common for one side of the brain to show more shrinkage than the other (asymmetric atrophy), which can cause specific behavioral patterns [6].
  • The Early-Stage Challenge: In the very early stages of bvFTD, an MRI might look “normal” to the naked eye [7]. This doesn’t mean the disease isn’t there; it may just be too early for the physical shrinkage to be obvious on a standard scan.

Measuring Brain Activity: The FDG-PET Scan

If an MRI is inconclusive, a doctor may order an FDG-PET scan. Instead of looking at the brain’s structure, this scan looks at its “fuel consumption.”

  • Hypometabolism: The scan uses a small amount of radioactive glucose to show which parts of the brain are using energy. In bvFTD, the frontal lobes and caudate nuclei (parts of the brain involved in habit and motivation) often show hypometabolism, meaning they are not using as much energy as they should [8][5].
  • The Diagnostic Edge: FDG-PET can often detect the disease earlier than an MRI because brain cells usually stop functioning correctly before they physically wither away [9].

The NfL Test: A Window into Cell Death

The most significant recent advancement in FTD diagnosis is the Neurofilament Light (NfL) test [10].

Neurofilaments are structural “cables” found inside healthy brain cells. When brain cells are damaged or die, these cables break and leak into the cerebrospinal fluid (CSF) and eventually the blood [11].

  • Differentiating from Mental Illness: This test is a game-changer for diagnosis. While primary psychiatric disorders (like depression or schizophrenia) can be severe, they do not typically cause brain cells to physically break apart and leak NfL [10][12].
  • High vs. Normal Levels: A high level of NfL in the blood or CSF is a strong signal that active neurodegeneration is happening [13]. A normal level, conversely, may point a doctor back toward a psychiatric cause or a “phenocopy” (a condition that looks like bvFTD but does not worsen over time) [14].

Key Terms for Your Next Visit

When speaking with the neurology team, using specific terms can help ensure you get the clearest answers:

  • “Is there evidence of frontoinsular atrophy?”: Asks specifically about the regions most linked to bvFTD.
  • “Can we order a plasma NfL test?”: Requests the blood-based version of the neurofilament test, which is less invasive than a spinal tap [10].
  • “Does the PET scan show frontal hypometabolism?”: Asks if the brain’s “activity map” shows the signature FTD pattern.
  • “Are we seeing longitudinal progression?”: Asks the doctor to compare current scans to previous ones to see if the shrinkage is getting worse over time [15].

Return to Home Page

Common questions in this guide

What does an MRI show in behavioral variant frontotemporal dementia?
An MRI can reveal atrophy, or physical shrinking, of the brain tissue. In bvFTD, this shrinkage typically occurs in the frontal and temporal lobes, though it may not be visible in the very early stages of the disease.
Why might a doctor order a PET scan instead of an MRI?
An FDG-PET scan measures brain energy activity rather than just physical structure. It can often detect bvFTD earlier than an MRI because brain cells typically stop functioning normally and use less energy before they actually shrink.
What is the NfL blood test for frontotemporal dementia?
The Neurofilament Light (NfL) test measures specific proteins that leak into the blood or spinal fluid when brain cells are damaged. High NfL levels strongly suggest active brain cell death, which helps doctors confirm neurodegeneration.
How do doctors tell the difference between bvFTD and mental illness?
Doctors use a combination of brain scans and biomarker tests to find physical evidence of disease. Unlike primary psychiatric conditions such as depression or bipolar disorder, bvFTD causes brain shrinkage and cell death that can be detected through MRIs, PET scans, and the NfL test.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Given the similarity to psychiatric symptoms, could we order a plasma Neurofilament Light (NfL) test to check for active neurodegeneration?
  2. 2.What did the MRI show regarding volume in the frontoinsular or mesial temporal regions?
  3. 3.If the MRI was inconclusive, would an FDG-PET scan help identify areas of low glucose metabolism in the frontal lobes?
  4. 4.Does the brain show any signs of 'asymmetric atrophy', and how does that relate to the current behavioral symptoms?
  5. 5.Could these symptoms represent a 'phenocopy syndrome' if follow-up scans show no change over time?

Questions For You

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References

References (15)
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    The Neuropsychiatric Features of Behavioral Variant Frontotemporal Dementia.

    Peet BT, Castro-Suarez S, Miller BL

    Advances in experimental medicine and biology 2021; (1281()):17-31 doi:10.1007/978-3-030-51140-1_2.

    PMID: 33433866
  2. 2

    Behavioral variant frontotemporal dementia in patients with primary psychiatric disorder: A magnetic resonance imaging study.

    Tafuri B, Filardi M, Frisullo ME, et al.

    Brain and behavior 2023; (13(4)):e2896 doi:10.1002/brb3.2896.

    PMID: 36864745
  3. 3

    Young-onset frontotemporal dementia in a homozygous tau R406W mutation carrier.

    Ng AS, Sias AC, Pressman PS, et al.

    Annals of clinical and translational neurology 2015; (2(12)):1124-8 doi:10.1002/acn3.265.

    PMID: 26734663
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    Neuropsychiatric Aspects of Frontotemporal Dementia.

    Younes K, Miller BL

    The Psychiatric clinics of North America 2020; (43(2)):345-360 doi:10.1016/j.psc.2020.02.005.

    PMID: 32439026
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    Neuroimaging in Frontotemporal Dementia: Heterogeneity and Relationships with Underlying Neuropathology.

    Peet BT, Spina S, Mundada N, La Joie R

    Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics 2021; (18(2)):728-752 doi:10.1007/s13311-021-01101-x.

    PMID: 34389969
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    Asymmetry of post-mortem neuropathology in behavioural-variant frontotemporal dementia.

    Irwin DJ, McMillan CT, Xie SX, et al.

    Brain : a journal of neurology 2018; (141(1)):288-301 doi:10.1093/brain/awx319.

    PMID: 29228211
  7. 7

    Microstructural grey matter alterations in patients with behavioural variant frontotemporal dementia.

    Akbarian B, Hett K, Phan T, et al.

    Brain communications 2025; (7(6)):fcaf427 doi:10.1093/braincomms/fcaf427.

    PMID: 41234527
  8. 8

    Data-driven analysis of regional brain metabolism in behavioral frontotemporal dementia and late-onset primary psychiatric diseases with frontal lobe syndrome: A PET/MRI study.

    Cagnin A, Pigato G, Pettenuzzo I, et al.

    Neurobiology of aging 2024; (137()):47-54 doi:10.1016/j.neurobiolaging.2024.01.015.

    PMID: 38422798
  9. 9

    The Evolving Role of FDG-PET in Behavioral Variant Frontotemporal Dementia: Current Applications and Future Opportunities.

    Ioannidis S, Konstantinidou N, Giannakis A, et al.

    International journal of molecular sciences 2025; (26(20)) doi:10.3390/ijms262010090.

    PMID: 41155382
  10. 10

    Biofluid biomarkers in distinguishing young-onset dementia from primary psychiatric disorders.

    Loi SM, Eratne D, Santillo AF, Velakoulis D

    Current opinion in psychiatry 2025; (38(2)):134-143 doi:10.1097/YCO.0000000000000979.

    PMID: 39887317
  11. 11

    Cerebrospinal fluid and blood neurofilament light chain levels in amyotrophic lateral sclerosis and frontotemporal degeneration: A meta-analysis.

    Verde F, Licaj S, Soranna D, et al.

    European journal of neurology 2024; (31(9)):e16371 doi:10.1111/ene.16371.

    PMID: 38937912
  12. 12

    Neurofilament light and cognition in community-dwelling non-Hispanic Blacks.

    Abdullah L, Zhang F, Hall J, O'Bryant S

    Journal of Alzheimer's disease : JAD 2024; (102(1)):60-66 doi:10.1177/13872877241283693.

    PMID: 39497299
  13. 13

    Urine as matrix for analysis of neurofilament light chain is not suitable to distinguish frontotemporal dementia from psychiatric diseases.

    van Engelen ME, Heijst H, Willemse EAJ, et al.

    Brain communications 2023; (5(2)):fcad120 doi:10.1093/braincomms/fcad120.

    PMID: 37101834
  14. 14

    The behavioural variant frontotemporal dementia phenocopy syndrome is a distinct entity - evidence from a longitudinal study.

    Devenney E, Swinn T, Mioshi E, et al.

    BMC neurology 2018; (18(1)):56 doi:10.1186/s12883-018-1060-1.

    PMID: 29704893
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    Utility of the global CDR® plus NACC FTLD rating and development of scoring rules: Data from the ARTFL/LEFFTDS Consortium.

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This page explains imaging and biomarker tests used to diagnose bvFTD for educational purposes. Always consult a neurologist for medical advice and to interpret your specific scan or lab results.

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