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Prosopagnosia -- also known as face blindness, or the inability to recognize familiar faces -- occurred across a range of degenerative and non-degenerative neurologic disorders, a large case series showed.

In a study of more than 300 patients with prosopagnosia, the temporal and occipital lobes and connecting fusiform gyrus were key brain areas involved, reported Keith Josephs Jr., MD, MST, MSc, of Mayo Clinic in Rochester, Minnesota, and co-author in .

"This is by far the largest study in the world on neurological diseases associated with prosopagnosia," Josephs told 番茄社区app. "In almost all instances, the right brain hemisphere was affected."

The case series also identified disorders not previously linked to prosopagnosia, Josephs said.

"One of the most important findings from the study is that loss of facial recognition in adulthood is not always permanent, but can be transient and may improve over time when associated with specific diagnoses -- for example, migraine headaches," he added.

The term prosopagnosia was first used in 1947, but a description of the disorder dates back to a case report in 1867, the researchers noted. "Prosopagnosia complicates recognition of faces of previously encountered individuals, especially unfamiliar faces (i.e., faces not often seen; e.g., high school classmates or prior coworkers) and also affects recognition of familiar faces (i.e., faces encountered more often; e.g., family members)," they wrote.

Prosopagnosia can be developmental or acquired, depending on whether onset occurs in early childhood or later. Acquired cases can have degenerative or non-degenerative etiology. Literature about prosopagnosia consists mainly of case reports and small case series.

The researchers identified 336 patients with probable or definite prosopagnosia in Mayo Clinic intake and referral center records from 2000 to 2023. They assessed regional involvement of the right and left frontal, temporal, parietal, and occipital lobes based on 18F-fluorodeoxyglucose PET or MRI scans. Median age at prosopagnosia onset was 66.

Probable prosopagnosia was defined as a subjective report of facial-recognition loss by a patient, caregiver, or partner without objective evidence. Definite prosopagnosia included objective evidence of prosopagnosia by formal or informal testing.

Ten patients (eight males) had developmental prosopagnosia, including one with Niemann-Pick disease type C and another with a FOXG1 mutation.

Of 326 cases of acquired prosopagnosia, 235 (72.1%) were categorized as degenerative and 91 (27.9%) as non-degenerative. The most common degenerative diagnoses were posterior cortical atrophy (21%), primary prosopagnosia syndrome (21%), Alzheimer's disease dementia (16%), or semantic dementia (11%). Among people with degenerative prosopagnosia, face blindness was stable or worsened over time.

In 117 patients with degenerative prosopagnosia who had PET, the temporal lobes were most frequently affected. In a subset of patients with degenerative prosopagnosia who died, the most common pathology findings were frontotemporal lobar degeneration with hippocampal sclerosis or mixed Alzheimer's and Lewy body disease pathology.

Non-degenerative diagnoses often were primary brain tumors (40%), ischemic or hemorrhagic infarcts (12%), or seizure-related diseases (12%). Five patients developed non-degenerative prosopagnosia immediately after a traumatic brain injury. Two other patients had visual snow syndrome, and two had attention deficit disorder.

In 82 patients with non-degenerative prosopagnosia who had MRI, a focal lesion affected the right temporal or right occipital lobe.

The researchers identified a group of patients with non-degenerative prosopagnosia whose face blindness improved or resolved. These were people with migraine-related prosopagnosia, posterior reversible encephalopathy syndrome, delirium, hypoxic encephalopathy, or ischemic infarcts.

"Two of the most interesting findings in patients with a non-degenerative diagnosis were the association of prosopagnosia with migraines and the observation that prosopagnosia can be transient and resolve over time," they wrote.

"Prosopagnosia as a feature of classic migraine is rarely described in the literature since the first report over two decades ago," they continued. "We did encounter patients with classic migraines in which the prosopagnosia was a feature of aura."

The study had several limitations, the researchers acknowledged, including its retrospective design. Not all patients completed a standardized objective test and prosopagnosia severity could not be determined.

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