Differentials
Alzheimer disease (AD)
SIGNS / SYMPTOMS
The physical exam does not reliably distinguish the conditions, because a normal exam is usually noted. One key feature that may differentiate FTD from AD is relative preservation of memory.
INVESTIGATIONS
Structural MRI typically shows regional losses in the temporoparietal regions in AD and the temporofrontal regions in FTD. CT shows global atrophy in AD, and focal atrophy in FTD.
Single-photon emission computed tomography (SPECT) or PET in early AD generally shows abnormality in the posterior cingulate and parietal lobes.[86]
Dementia with Lewy bodies (DLB)
SIGNS / SYMPTOMS
DLB is characterized by predominance of amnesia, fluctuation in cognition, visual hallucinations, and parkinsonism in the early stages of the illness.
Personality and comportment are relatively preserved.
Visual hallucinations are very rare in FTD.[87]
INVESTIGATIONS
MRI/CT shows global atrophy in DLB, and focal atrophy in FTD.
SPECT or PET in early DLB generally shows abnormality in the parietal and occipital lobes.[86]
Vascular dementia
SIGNS / SYMPTOMS
Vascular dementia may mimic FTD by presenting with prominence of apathy, executive dysfunction, or behavioral disorder (impulsiveness and irritability), and relative preservation of memory.
INVESTIGATIONS
Brain MRI or CT will show evidence of cerebrovascular pathology; lacunes in the basal ganglia and thalamus; or marked gliosis of the frontal, subcortical, and deep white matter.
Bipolar disorder
SIGNS / SYMPTOMS
Episodes of mania and depression typically begin in the third decade of life and show complete remission between episodes. When late-onset mania occurs after age 60 years it is attributable to brain diseases (cerebrovascular, trauma, neoplasm, drug withdrawal and/or intoxication) in >80% of cases.
INVESTIGATIONS
Brain imaging is generally normal in bipolar disorder.
Major depression
SIGNS / SYMPTOMS
Major depression is characterized by the marked predominance of sad mood, anhedonism, hopelessness, suicidal thoughts, psychomotor retardation, insomnia, and self-deprecating and pessimistic mental states. Most likely to be confused with the apathetic type of FTD.
INVESTIGATIONS
Brain imaging is generally normal in major depression.
Obsessive-compulsive disorder (OCD)
SIGNS / SYMPTOMS
Onset of OCD is typically in the second or third decade of life. Remission may not be complete between episodes but OCD can be distinguished by long history and association of compulsions with preserved insight and marked anxiety. Patients with early-onset dementias often try to cope with their cognitive impairment by imposing order on the threat of chaos.
INVESTIGATIONS
Brain imaging is generally normal in OCD.
Substance use disorders
SIGNS / SYMPTOMS
States of intoxication from stimulants, alcohol, and other agents may mimic FTD by producing euphoria, disinhibition, impulsiveness, and poor judgment, but these states are usually transient.
Track marks and puncture sites may be visible on arms, legs, and neck, along the course of superficial veins.
INVESTIGATIONS
Serum and urine toxicology will usually identify the substance involved.
Primary brain tumor
SIGNS / SYMPTOMS
The cognitive manifestations of brain tumor depend on location.
Tumors in the frontal lobes may present with decreased attention and alertness, executive dysfunction, and impaired social judgment.
Tumors in the temporal lobes may present with nonfluent aphasia and memory disorder.
INVESTIGATIONS
Brain imaging will show tumor, and may also show a penumbra of edema and compression of adjacent brain structures.
Hyperthyroidism
SIGNS / SYMPTOMS
Features of hyperthyroidism, such as irritability, restlessness, increased eating (with decreased satiation), and distractibility, may result in a presentation that mimics FTD.
INVESTIGATIONS
Low blood levels of thyroid-stimulating hormone and increased levels of free thyroxine are typical of hyperthyroidism.
Normal pressure hydrocephalus
SIGNS / SYMPTOMS
Features of fronto-subcortical profile with psychomotor slowing and executive function deficits, such as decreased word fluency, may mimic FTD.
INVESTIGATIONS
Brain imaging will show general enlargement of all four ventricles.
HIV dementia
SIGNS / SYMPTOMS
Features such as apathy, behavioral disturbances, and depression may mimic FTD.
INVESTIGATIONS
Serology test is positive for HIV.
Neurosyphilis
SIGNS / SYMPTOMS
Meningismus, fever, and cranial nerve palsies are typical. Rapidly progressive dementia with personality changes that mimic FTD but presence of cranial nerve abnormalities (II, III, IV, VI, VII, and VIII) and uveitis point to syphilis. Psychiatric manifestations may be present.
INVESTIGATIONS
Venereal disease research laboratory tests (blood and CSF). The fluorescent treponemal antibody-absorbed (FTA-ABS) test has high sensitivity and if negative excludes a diagnosis of neurosyphilis. MRI lesions in temporal lobes disappear with treatment.
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