Inappropriate sexual behaviors are not specific to one cause of dementia [26] but often present in FTD [27]. They can be seen at all stages irrespective of age, age at onset, gender, and educational level [28]. They include excessive sexual comments, hugging/kissing/preoccupation with sex, masturbation in public, sexual hallucinations, addiction to Internet pornography, delusions of spousal infidelity, attempting to seduce/chasing people for sexual purposes, disrobing in public, and changes in sexual preference (paraphilic-related disorder). Some behaviors may be inappropriate only because they are performed publicly and may result from compulsive disinhibition rather than an increase in libido [29]. Paradoxically, in a systematic assessment of changes in sexual behavior in bvFTD, SD, and AD, bvFTD patients showed prominent hyposexual behaviors, including decreased affection, initiation, and response to advances by partners and decreased frequency of sexual relations, as compared to AD and SD patients. Notably, aberrant or unusual sexual behaviors were reported in a minority of bvFTD and SD patients and occurred in patients who also showed hyposexual behavior toward their partner [30].

Changes in sexual behavior are due to hormonal changes, disruption of interconnected brain structures (hypothalamus, amygdaloid nuclei, inferior frontal cortex, and medial striatal/septal region), or both [31]. Sexual disinhibition could also be induced by blockade of either 5-HT2 receptor (selective serotonin reuptake inhibitors may suppress sexual drive), alpha-2 adrenergic receptor, or both [32]. Medical care providers need to be trained to discuss these potential issues with patients and carers and to provide solutions to cope with these difficulties [26]. Inappropriate sexual behaviors in the context of dementia are covered in another chapter of this book.

Loss of manners or decorum includes behaviors that violate social graces such as inappropriate laughter, cursing or loudness, offensive jokes or opinions, failing to wait in the line, and impolite physical behaviors (eating with mouth open, or putting a finger up the nose, flatulence, scratching private parts, picking teeth, belching, or spitting, etc.) [16]. Milder symptoms are loss of respect for interpersonal space or propensity to continue talking despite others’ attempts to end a conversation.

Impulsive rash or careless actions include dangerous driving, new-onset gambling, stealing (usually food or “shiny” objects), buying or selling objects without regard for consequences, or indiscriminate sharing of personal information [16].

Criminal violations can go from petty theft or running stop signs and traffic lights to child molestation, including pedophilic behavior. Patients with early FTD who commit criminal violations present a challenge to the criminal justice system since they have clear consciousness and normal global cognition, and one has to consider alterations in moral cognition before ascribing criminal responsibility [33]. An important finding is that these patients are aware of the social rules, but their moral reasoning is defective, and they have difficulties in detecting violations of these rules. They understand the nature or their acts and the potential consequences, but do not feel concerned enough to be deterred. Criminal behavior in FTD may involve a unique combination of lesions. Alterations in the ventromedial prefrontal cortex may alter moral feelings, lesions in the right anterior temporal cortex may induce loss of emotional empathy, and orbitofrontal changes can cause disinhibited, compulsive behavior [33].

The patients no longer give the reassuring facial signals that there is social interaction. Neither do they show any feeling. They can appear hostile and can induce unease in others [9].

Antisocial acts, sometimes called “sociopathic,” are frequent in FTD, including stealing, hit and run accidents, physical assault, indecent exposure, public urination, inappropriate sexual behaviors, shoplifting, eating food in grocery store stalls, breaking and entering into other’s homes, driving violations, nonpayment of bills, and acts of violence. All these may be linked to ventromedial and orbitofrontal lesions of the frontal lobes. FTD patients may know right from wrong and understand the nature of their acts clearly enough so that they could be held legally culpable [34]. These behaviors result from a combination of diminished emotional concern for the consequences of their acts and disinhibition consequent to right frontotemporal dysfunction. In many jurisdictions, FTD patients committing sociopathic acts would not pass legal criteria for “not guilty by reason of insanity” [34].

Lastly educational level shows an influence on disinhibition [35]. Primarily studied in AD, the cognitive reserve hypothesis states that reserve mechanisms provided by high education and adult occupation could work against pathological process [36]. Likewise, in FTD, patients with a higher reserve seem to require a more severe extent of neuropathology to develop behavioral disinhibition and loss of self-control. The term “behavioral reserve” has been proposed to designate the putative protection provided by education [37].

Apathy refers to a loss of motivation, interest, or initiative (motor, cognitive, and affective) [38]. It differs from inertia defined as the need for prompts or cues to initiate or continue activities [16]. The absence of apathy is uncommon in FTD, though it can be a distinctive feature of some C9orf72 mutations [39]. Most FTD patients disengage from usual activities, which add to carers’ emotional and physical distress [40]. Apathy, coexisting with personal neglect and memory complaints, frequently contributes to a misdiagnosis of depression. However, suicidal ideation and guilt are noticeably absent in FTD. Apathy may not coexist at all with depressive symptom but instead be associated with disinhibition, restlessness, and socially inappropriate behavior [9]. The Social Cognition and Emotional Assessment clearly distinguishes FTD (with low scores) from major depressive disorder [41]. Apathy is the focus of another chapter of this book.

Sympathy and empathy correspond to the perception, understanding, and reaction to the distress or need of another person. While sympathy merely reflects the ability to express a similar emotional tone or to be moved by another person, empathy requires to put oneself in the other person’s situation and to share feelings as if they were experienced by the self [42]. Sympathy and apathy have three components: (i) affective, i.e., sharing and responding to the emotional experience of others; (ii) cognitive, i.e., understanding the intentions and perspectives of others; and (iii) moral, i.e., judgments about the wrongness of an action or the punishment that a perpetrator deserves [43]. Empathy and sympathy are driven by a switch in viewpoint, from a personal perspective to the perspective of a person or a group who is in need. As such, they are a component of social cognition described by the Theory of Mind (ToM). The ToM is the ability to infer mental states, thoughts, and feelings of others and to understand that they can differ from one’s own [44]. Lack of sympathy and empathy affects the social functioning of patients. Ability to recognize violations of social norms, moral and social reasoning (i.e., to integrate social knowledge with its affective connotations), facial emotions (especially anger and disgust), emotional prosody, and body gestures is frequently impaired in bvFTD [45].

Loss of sympathy manifests as emotional blunting or indifference, which is a source of distress for family members [46], and contributes to institutionalization. Using questionnaires, emotional blunting is better assessed by the carer than by the clinician and can distinguish patients with bvFTD from those with AD [47]. Emotional blunting is associated with right anterior temporal atrophy [48].

Early perseverative stereotyped behavior is typical and frequent in FTD. Stereotypies can be simple (tapping, clapping, rubbing, humming, repetitive utterance, etc.), sometimes self-injurious (trichotillomania, picking at fingertips to the point of causing excoriation), or complex (counting, collecting, hoarding, repetitive trips to the bathroom without need, etc.). Stereotypical movements are repetitive coordinated movements that resemble purposeful acts but have no clear purpose. Tics are usually more abrupt and driven, and compulsions are usually more complex routines and rituals [49]. Contrary to obsessive-compulsive disorders, preventing patients with bvFTD from making ritualized activities (by engaging them in another activity) does not generate anxiety. The bvFTD patients do not justify their perseverative behavior like patients with obsessive-compulsive disorders, who usually feel that it will somehow prevent a dreaded event from occurring or invading their thoughts. Socially embarrassing or disturbing stereotyped behaviors can be controlled by directing patients to routine tasks such as puzzles, crosswords, or hidden words.

In some cases, continuous walking or roaming can lead patients to a great distance from home (which does not necessarily mean they are lost) with significant physical fatigue and dehydration. An electronic bracelet can be useful in such cases to help in locating the subject. Young patients can invest excessively in sport and they must be supervised to avoid exhaustion.

Patients with bvFTD generally display changes in their dietary and eating habits. They usually eat more, with appetite for sweets or specific food, e.g., bananas or pieces of sugar. Hyperphagia may be preceded by weight loss related to obsessive use of diet pills and fiber aids, or selection of food (e.g., eating white food only), preventing a balanced diet. Food selection is specifically observed in the semantic variant of FTLD. Patients often eat greedily, which may cause choking, and with time they can start mouthing inedible objects. Changes in dietary habits may also concern drinks (alcohol, soft drinks, or water). Patients may seek to drink in secret, in a childish and clumsy manner. This behavior may become life-threatening (e.g., liver damage, diabetes, or severe hyponatremia), requiring appropriate environmental measures, such as filling wine bottles with grape juice, shutting off the water supplies when leaving the house, etc. With progression of the disease, apathy increases and patients stop looking for food and eating greedily. Ultimately they will even need to be encouraged to eat. However, hyperorality and mouthing behaviors are a durable symptom.

Hallucinations and delusions are uncommon in FTD as compared with other causes of dementia [52]. The prevalence rate of psychosis is 10–15 % in this population [53]. It is more frequent in some familial genetic forms of the disease [54]. When present, they raise the probability of a misdiagnosis of psychiatric disorder. In addition, many FTD patients present with unexplained somatic complaints, including worries about bowel function [55].

Delusions may occur at an early stage of FTD and can even be the presenting symptom. Rarely persecutory, somatic, or religious delusions or delusions of jealousy are rather observed. Delusions often have a bizarre content [9, 56–58].

Paranoid thoughts and delusions of spousal infidelity, visual hallucinations, and misidentification are described in patients with GRN mutation [59]. For instance, zooptic hallucinations were a salient feature of a late-onset phenotype resembling dementia with Lewy bodies (DLB), with visuospatial impairment, fluctuations, parkinsonism, and complex misidentification syndrome [60]: a patient with a family history of dementia presented with Fregoli’s delusion, a delusional belief that different persons were in fact a single person who changed appearance. There were no major cognitive or behavioral symptoms of the frontal type. The MRI scan showed diffuse cortical and subcortical atrophy, particularly in temporal and frontal regions with prevalence on the right hemisphere. The FDG-PET scan showed severe bilateral frontal hypometabolism extending to both parietal and temporal cortices, more pronounced on the right hemisphere. AD CSF biomarkers were within the normal ranges, but plasmatic progranulin level was very low. A GRN mutation was confirmed by genetic testing.

Up to 38 % of patients with C9orf72 mutations present with psychotic symptoms including mystic delusion, resulting in initial psychiatric diagnoses such as delusional psychosis, somatoform psychosis, or paranoid schizophrenia [61]. A further 28 % of patients with the same mutation exhibit paranoid, deluded, or irrational thinking, which are much rarer in patients without such a mutation. This led to the hypothesis that beyond FTD, C9orf72 mutations could also be a cause of late-onset psychosis. A case report of a 44-year-old man bearing a C9orf72 mutation is interesting in that regard [62]: this man was referred for a mystical delusion and visual and auditory hallucinations. There was no family history of dementia or psychiatric disorders. He was diagnosed with “delusional hallucinatory psychosis,” though a treatment with haloperidol brought no benefit. He did not show neurological symptoms for 7 years, and no atrophy nor hypometabolism was evident in neuroimaging. Mystical grandiose delusions with auditory hallucinations remained poorly controlled despite a switch for clozapine. Other case reports include a woman with delusion of pregnancy [63], a man complaining of having pieces of plastic emaning from his head, and a woman who had visions of the devil and developed strategies for keeping him at bay. Another patient had a mono-deluision of weakness of the gluteal muscles, prompting him to maintain his finger in his anus to prevent incontinence [61]. In the same article, the case of a patient with delusional parasitosis believing that he was infested by mites crawling under his skin and into his extremities is also reported. As the mites seemed to congregate in his earlobe, he could reduce their number by pinching his earlobe at regular 10-min intervals [61]. Lastly, a woman reported to the police that a man dressed in a gorilla outfit hid in her garden, and a man was convinced that had been contacted by letter or phone by dead friends and hatched plans to meet them.

Most of these patients had clinical or imaging FTD features [64]. However, long-lasting psychosis with no imaging abnormalities that did not meet the criteria for possible bvFTD has been described in patients with C9orf72 mutations [39, 65]. When parkinsonism is associated, and in the absence of motor neuron disease, the differential diagnosis of DLB is raised [66, 67]. Psychotic features including hallucinations and delusions are common in DLB, visual hallucinations being a core feature. However, there is no evidence for repeat expansions in the C9orf72 gene in DLB [68].

Tau gene mutations give a wide range of phenotypes including progressive psychosis [57] that may precede bvFTD features [58]. A patient bearing a mutation in MAPT obtained a bachelor’s degree in Engineering Technology at age 22. By that time, he became socially withdrawn, argumentative, and difficult. By age 25, he had lost his job as a teacher and was described as obstinate and emotionally blunted. He then developed stereotypical behavior. On neuropsychological assessment, he showed borderline intellectual functioning and a below-average memory performance. An MRI scan of the brain showed marked atrophy of the frontal lobes. Neurological examination was normal, and psychiatric evaluation revealed symptoms of psychosis that were not typical of schizophrenia. At age 27, further examination showed a reduced attention span and difficulties with simple abstract reasoning. The social conduct deteriorated significantly with disinhibition, theft, and violation of interpersonal space. He developed hyperorality and difficulties swallowing at age 33 and died of aspiration pneumonia at age 36.

As a whole, patients with C9orf72 mutations and/or the corresponding pathology (FTD-TDP43 type B) are more likely to show psychosis than those with other pathologies. Patients with FTD-FUS pathology may also show psychosis [53].

Behavioral changes are subtler and less socially disruptive in the language variant of FTD than in bvFTD. They are more obvious in semantic dementia, where the main characteristic changes are preference for routine; activity limitations to a few that may, however, involve complex sequences of procedure and require some skills and executive functions; stereotyped behavior; parsimony; loss of empathy; change in food preference; and lack of awareness of danger [69].

At follow-up, patients with semantic aphasia may develop severe agitation linked to their misunderstanding of the environment, which can mimic psychosis [70].

FTD and schizophrenia share clinical features, especially related to negative symptoms (e.g., blunted affect, apathy, social withdrawal). However, disinhibition, overeating, mutism, or incontinence is not observed in typical schizophrenia, and antipsychotic treatment is not effective in FTD. The morbid risk for schizophrenia in first-degree relatives is higher in relatives of probands with FTD than in relatives of probands with AD. Moreover, in some families with both FTD and schizophrenia, the causal FTD mutation was also present in individuals with schizophrenia. This could indicate a common etiology for both conditions in some families [80]. Vulnerability to psychosis in FTD and schizophrenia might share a common pathophysiology involving alterations in the frontal cortex and thalamus [53].