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When Hippocampal Volume Is Normal: Other Dementias to Consider

If your loved one's brain scan shows a normal-sized hippocampus, it does not rule out dementia. Several other types of dementia—and even treatable conditions—can cause cognitive decline without shrinking this key memory center. This article walks you through what to look for, what to ask the doctor, and how to prepare for a more accurate diagnosis. You are not alone, and there are concrete steps you can take to get clearer answers and better support.

Key points

  • A normal hippocampal volume does not rule out dementia; many other types affect different brain regions first.
  • Always rule out reversible causes (depression, thyroid, B12, medications, subdural hematoma, NPH) before accepting a dementia diagnosis.
  • Frontotemporal dementia, Lewy body dementia, and vascular dementia have distinct early symptoms that differ from Alzheimer's.
  • Keep a detailed symptom journal and bring it to every appointment to help the doctor see patterns.
  • Seek a specialist (neurologist, geriatric psychiatrist, memory clinic) for a thorough evaluation, including neuropsychological testing and advanced imaging if needed.
  • The diagnosis may change over time as symptoms evolve; focus on managing current symptoms and planning for the future.

Why a Normal Hippocampus Doesn't Mean 'No Dementia'

The hippocampus is a small, seahorse-shaped region deep in the brain that is critical for forming new memories. In Alzheimer's disease, it is often one of the first areas to shrink, which is why doctors look for hippocampal atrophy on MRI scans. However, many other dementias—and even reversible conditions—can cause significant cognitive problems while leaving the hippocampus relatively untouched. As Teepa Snow explains, for a dementia diagnosis there must be damage to at least one other brain area beyond the hippocampus, such as the frontal lobes, language centers, or visual processing regions. So a normal hippocampal volume simply shifts the focus to other possible causes.

Common Dementias That May Spare the Hippocampus

Frontotemporal dementia (FTD) often begins with changes in personality, behavior, or language rather than memory, and the hippocampus may remain normal in early stages. Lewy body dementia (LBD) is marked by visual hallucinations, fluctuating attention, and Parkinson-like movement problems; memory can be relatively preserved compared to Alzheimer's. Vascular dementia results from reduced blood flow to the brain, often due to small strokes, and its symptoms depend on which brain regions are affected—memory may not be the first or only issue. Mixed dementia, where more than one type of pathology is present, is very common in older adults, especially those over 80. In all these cases, a normal hippocampal scan does not rule out dementia.

Reversible or Treatable Conditions That Mimic Dementia

Before settling on a dementia diagnosis, doctors must rule out conditions that can look like dementia but are potentially reversible. These include depression (which can cause memory complaints and lack of motivation), hypothyroidism, vitamin B12 deficiency, medication side effects, hearing or vision loss that leads to confusion, and chronic subdural hematoma (a collection of blood on the brain's surface after a fall). Normal pressure hydrocephalus (NPH) is another treatable cause, where excess spinal fluid builds up and causes gait problems, urinary incontinence, and cognitive decline—sometimes improved by a shunt. Alcohol-related dementia and HIV-associated dementia can also improve with treatment. As one source notes, 'dementia is a diagnosis of exclusion,' meaning all these possibilities should be checked first.

General caregiving information, not medical advice. Check medications and major care changes with your clinician.

Step-by-step

  1. 1. Request a full medical workup, not just a brain scan. Ask your doctor to order blood tests for thyroid function, vitamin B12, and syphilis screening, and to review all medications for side effects that could cause confusion. This is the first step to rule out reversible causes.

  2. 2. Keep a symptom journal for two weeks before the next appointment. Write down specific examples of changes you notice: when they happen, what the person was doing, and how long they last. Include any falls, hallucinations, mood swings, or trouble with walking. This helps the doctor see patterns that point to specific dementia types.

  3. 3. Ask for a referral to a specialist—a neurologist, geriatric psychiatrist, or memory clinic. General practitioners may not have the time or tools to differentiate between dementia types. Specialists can perform detailed cognitive testing and advanced imaging (like PET scans or functional MRI) to look for damage in other brain regions.

  4. 4. If the doctor mentions 'normal pressure hydrocephalus,' ask about the 'classic triad' of symptoms: gait difficulty (feet feel stuck to the floor), urinary urgency or incontinence, and cognitive slowing. A lumbar puncture (spinal tap) that temporarily improves walking can help confirm the diagnosis.

  5. 5. For possible Lewy body dementia, watch for three core features: visual hallucinations (seeing people or animals that aren't there), fluctuations in attention (good days and bad days, or even good hours and bad hours), and Parkinsonism (shuffling walk, stiffness, tremors). Report these to the doctor, as they are often missed.

  6. 6. If frontotemporal dementia is suspected, note changes in personality or behavior first—loss of empathy, compulsive behaviors, inappropriate social comments, or a sudden change in food preferences. Memory may seem fine early on. Share these observations with the clinician.

  7. 7. Consider a neuropsychological evaluation—a 2-4 hour battery of tests that maps out strengths and weaknesses in memory, language, attention, executive function, and visual-spatial skills. This can reveal a pattern that points to a specific dementia type, even when the hippocampus looks normal.

  8. 8. Ask about a PET scan or amyloid imaging if available. These scans can detect Alzheimer's pathology (amyloid plaques or tau tangles) even when the hippocampus is normal. A negative amyloid scan makes Alzheimer's unlikely and pushes the diagnosis toward other causes.

  9. 9. If the diagnosis remains uncertain, accept a provisional label like 'mild cognitive impairment' or 'dementia, type unspecified.' As one source notes, the diagnosis can change over time as symptoms evolve. Focus on managing current symptoms and planning for the future rather than forcing a label.

  10. 10. Bring a list of all current medications (including over-the-counter and supplements) to every appointment. Some drugs, like anticholinergics (found in many sleep aids, allergy meds, and bladder control drugs), can cause cognitive impairment that mimics dementia. Ask the doctor if any could be reduced or stopped.

What not to do

  • Do not assume a normal MRI means 'no dementia.' Many dementias do not shrink the hippocampus early on. Instead, ask the doctor: 'What other tests can we do to look for damage in other parts of the brain?'

  • Do not ignore sudden or fluctuating symptoms. If your loved one has good days and bad days, or if symptoms came on over weeks rather than years, this could point to Lewy body dementia, delirium, or a reversible cause like a subdural hematoma. Report these patterns immediately.

  • Do not accept a diagnosis of Alzheimer's without a thorough evaluation, especially if memory is not the main problem. Many people are misdiagnosed with Alzheimer's when they actually have FTD, LBD, or vascular dementia. Push for a specialist opinion.

  • Do not stop investigating if the first doctor says 'it's just aging.' Significant cognitive decline is not normal aging. As Teepa Snow says, if a change is creating a disability in daily function, it deserves a full workup. Get a second opinion if needed.

  • Do not forget to check for depression. Depression can cause memory complaints, lack of motivation, and social withdrawal that looks like dementia. Unlike dementia, people with depression often worry about their memory and may improve with treatment. A geriatric psychiatrist can help differentiate.

Practical tools

  • Symptom Tracking Sheet

    Create a simple log with columns for date, time, specific behavior (e.g., 'could not find the bathroom,' 'saw a cat that wasn't there'), what was happening before, and how long it lasted. Bring this to every doctor visit. It helps the clinician see patterns that point to specific dementia types.

  • The 'Get Up and Go' Test for NPH

    Ask your loved one to stand up from a chair without using their arms, walk 10 feet, turn, and sit back down. If they have trouble starting to walk, take small shuffling steps, or feel unsteady, mention this to the doctor. It is a simple screening for normal pressure hydrocephalus.

  • Medication Review Checklist

    List every drug (prescription, OTC, supplements) with dose and frequency. Use an online tool like the Anticholinergic Cognitive Burden Scale (available free) to check if any are 'highly anticholinergic.' Share this with the pharmacist or doctor to identify potential culprits.

  • Phrases to Ask the Doctor

    If the MRI is normal, say: 'Since the hippocampus looks okay, what other tests can we do to find out what is causing these symptoms? Could it be frontotemporal dementia, Lewy body dementia, or vascular dementia? Should we consider a PET scan or neuropsych testing?'

  • The 'Three Questions' for Possible Reversible Causes

    Ask the doctor: (1) 'Has she had any falls recently?' (to check for subdural hematoma), (2) 'Could her medications be causing this?' (to review anticholinergics, sedatives, etc.), and (3) 'Has she been screened for depression, thyroid problems, or vitamin deficiencies?'

  • Support Group for Rare Dementias

    Organizations like the Association for Frontotemporal Degeneration (AFTD) and the Lewy Body Dementia Association offer free resources, helplines, and online support groups. They can help you understand the specific challenges of these less common dementias.

Discuss with your clinician

Ask your doctor: 'Could my loved one have a reversible cause like normal pressure hydrocephalus, and should we consider a lumbar puncture to test for it?'

Discuss: 'What are the risks and benefits of a PET scan or amyloid imaging for our situation? Would it change our treatment plan?'

If antipsychotic medications are suggested for hallucinations or agitation, ask: 'Is this safe for someone with possible Lewy body dementia? Are there alternatives?'

Inquire: 'Should we see a neuropsychologist for a full cognitive evaluation to help pinpoint the type of dementia?'

Ask: 'Are there any clinical trials for the suspected dementia type that my loved one might be eligible for?'

Related guides

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