Pathogenesis Some patients are associated with mutations in the tau gene. Clinical manifestations Semantic dementia, also known as temporal variant of FTLD (tvFTLD), accounts for 40% of frontotemporal lobar degeneration. It is characterized by progressively worsening semantic memory and comprehension deficits. Patients lose memory for semantic knowledge of words, objects, and people, and exhibit severe naming and comprehension deficits, such as the inability to name objects such as buttons and toothbrushes, and lose memory for their functions as the disease progresses. The patient’s spontaneous language is fluent, but the speech is hollow and lacks real words, often using “something” to refer to specific objects and “do” to refer to specific behavioral actions. There may be behavioral changes, often showing compulsive, stereotyped behavior. The impairment in language function lasts for at least 2 years or more before a general decline in intelligence occurs, and other cognitive abnormalities appear as the disease progresses. Primitive reflexes, motor inability, tonicity, and tremor appear late in the course of the disease. Ancillary tests Routine blood, urine and cerebrospinal fluid tests are normal. Neuropsychological assessment and brain imaging are useful for diagnosis and differential diagnosis. 1. Neuropsychological assessment: Neuropsychological assessment can help make diagnosis and differential diagnosis. Tests related to semantic abilities are commonly used, including picture naming, word-picture matching, description-naming, word definition tasks (e.g., presenting “duck” and asking the participant to give a description of “living in water, flat beak”), categorization tasks (e.g., presenting “lion and mouse” and asked whether they belonged to the same category), and semantic category fluency tests, patients were significantly worse than normal. Situational memory, perception, and spatial structure ability tests were relatively good, but semantic impairment often affected other cognitive tests, such as asking patients what season they are in, and patients could not answer because they did not understand the meaning of the season. 2.Brain imaging Semantic dementia: Atrophy of the anterior temporal lobe is seen, with dominance focusing on the non-dominant side.PET or SPECT shows reduced metabolism in the corresponding area, which appears earlier and is more sensitive than MRI. Diagnostic criteria Criteria for semantic dementia 1. Description of clinical features: Semantic (understanding of word meanings and object discrimination) impairment is the earliest and most prominent symptom and is present throughout the course of the disease. Other cognitive functions including memory are not impaired or are relatively preserved. 2. Core diagnostic features: (1) Invisible onset and gradual progression. (2) Language impairment with the following features: spontaneous speech as fluency, speech hollowness, and continuous progression; memory loss for word meanings, manifested as naming and comprehension impairment; semantic mispronunciation. (3) Sensory-perceptual impairment: Facial loss of recognition Recognition and discrimination impairment of familiar faces; Joint loss of recognition Discrimination impairment of objects. (4) Preservation of perceptual matching and picture regeneration. (5) Retention of the ability to retell individual words. (6) Relative preservation of the ability to read aloud and dictate common words. (3) Supporting diagnostic symptoms: (1) Speech and language: compulsive language; use of idiosyncratic vocabulary; no phonological mispronunciation; can read aloud but does not understand what is being read aloud; normal computation. (2) Behavioral disorders: lack of empathy; narrow interests, prejudice; stinginess. (3) Somatic symptoms: no or primitive reflexes, motor inability, tonicity and tremor in the late course of the disease. (4) Laboratory tests: (1) Neuropsychological: significant semantic deficits, inability to understand the meaning of words, to name or identify objects and faces; normal phonology and grammar, normal perceptual processing. (2) Electroencephalogram: normal. (3) Brain imaging (structural or functional): significant anterior temporal lobe abnormalities (symmetric or asymmetric). 5. Exclusion criteria: (1) History and clinical manifestations: acute onset, triggered by an acute event; traumatic brain injury associated with the onset; early severe memory impairment; spatial disorientation; nervous and panicked speech, disorganization; myoclonus; cerebellar symptoms; choreoathetoid tardive dyskinesia. (2) Laboratory tests: brain imaging shows lesions mainly involving structures behind the central sulcus or multiple foci; laboratory tests suggest metabolic or inflammatory lesions such as MS, syphilis, AIDS, and herpes simplex encephalitis. Differential diagnosis It should be differentiated from other disorders with significant psychobehavioral or speech disorders (including Alzheimer’s disease, Lewy body dementia, schizophrenia, depression, and other causes of simple aphasia). Points of differentiation are the order of appearance of behavioral symptoms, language disorders, and other cognitive impairments, as well as ancillary tests such as neuropsychological assessment and imaging. Treatment Cholinesterase inhibitors are usually ineffective; excitatory amino acid antagonists have shown some improvement. Selective 5-HT reuptake inhibitors can reduce disinhibition, impulsivity, repetitive behaviors, and eating abnormalities. Small doses of Valium or atypical antipsychotics may be given to patients with irritable, agitated, and aggressive behavior, but should be started at low doses and slowly increased, using the smallest effective dose possible.