Memantine resolves inappropriate sexual behavior in an elderly male with intellectual disability.

Abstract

<h3>Introduction</h3> Memantine is a non-competitive N-methyl-d-aspartate receptor antagonist approved for the treatment of moderate to severe Alzheimer's disease. Given its connection with glutamate pathways, memantine is effective in many psychiatric conditions as monotherapy and as an adjunct. Inappropriate sexual behavior (ISB) incorporates sex talk, implied sexual behavior (openly reading pornography, requesting unnecessary genital care) and sexual acts (touching, grabbing, exposing, masturbating) privately or publicly. Hypersexuality has been regarded as a form of obsessive compulsive disorder. There is a dearth of literature about ISB in individuals with intellectual disability (ID), and diagnosing major neurocognitive disorder (NCD) is difficult, due to the lack of standardized diagnostic criteria. In this population, NCD is suspected in the context of new onset cognitive impairment, behavior disturbance and a functional decline. The prevalence of behavioral and psychiatric symptoms of minor and major neurocognitive disorders is 50–80 %, respectively. This patient was initially diagnosed with NCD and memantine was initiated. However, clinical follow ups and serial, stable Montreal Cognitive Assessments (MOCA) over three years, did not support this diagnosis. <h3>Methods</h3> Casereport of a male with ID who manifested novel, ISB at age 67. This includes history, clinical follow ups, physical and cognitive evaluation, neuroimaging, laboratory (lab) tests, literature review using PubMed. ISB uncontrolled with various pharmacologic agents eventually resolved with the addition of memantine which was gradually increased to 10 mg twice daily (BID). When a recurrence of ISB occurred after two years, it remitted with memantine 25 mg (administered in two divided doses). <h3>Results</h3> A67 year-old, single, white male with ID, hypertension, diabetes type 2 and hyperlipidemia who followed up in psychiatry for intermittent explosive disorder and anxiety, was stabilized on citalopram 40 mg daily (QD) and gabapentin 300 mg thrice daily (TID). He had special education through 12th grade and an intelligence quotient of 68. New onset ISB toward men was reported on January 2016. Episodes occurred in communal areas involving the touching of penises with pants down, propositioning someone at a public pool, and placing himself very close to a man during a class. Due to complaints, a team with a behaviorist was formulated to assist in preventing triggering of sexual impulse. Gabapentin was progressively increased to 600 mg TID; later risperidone was initiated, then increased to 0.5 mg BID in combination with citalopram 40 mg. Thereafter, the undesirable behavior gradually subsided. MOCA was 16/30. Labs included: creatinine; 1.28mg/dl (N<1.34mg/dl), GFR; >60ml/min(N), fasting glucose; 129mg/dl (N60-99mg/dl), vitamin B12; 291pg/ml(N>200pg/ml), vitamin B1; 75 nmol/L (N70-180 nmol/L), Methylmalonate, MRI and other dementia related labs were unremarkable. Vitamin B1 and B12 were started. Although ISB had ceased, the patient was seen again after two months due to progressive unsteadiness, falls, slurred speech and worsening cognition after gabapentin was increased. Mini mental status examination was 17/30. Memantine 5 mg daily was initiated and Gabapentin was gradually decreased to 300 mg QD. After two months, improved cognition with resolution of ISB was reported. After two years of stability, he began pursuing a man obsessively in a sexual manner over a two-month period. When examined on April 2019, his MOCA was 16/30 with stable labs. Memantine was increased to 10 mg in am and 15 mg at pm to target ISB. After 44 days, ISB was reported to have resolved soon after increasing memantine. At this visit, escitalopram 15 mg replaced citalopram 40 mg QD due to safety concerns. Sustained remission of ISB was reported in January, 2020. In March 2020, patient was seen again as he had touched a female inappropriately a few times during pool classes. MOCA was 18/30 (increased by two-points). He admitted to experiencing slight urges, but later quit the class and declined to attend the Pride parade to curb temptation. Although he had age related physical decline, there was no evidence of cognitive or functional impairment compared to baseline. Subsequently, the diagnosis of major neurocognitive disorder (NCD) was questioned. Additionally, he had demonstrated insight and successfully resolved ISB. To date, his ISB is in remission with stable labs. <h3>Conclusions</h3> Resolution of ISB in a patient with ID is a previously unreported therapeutic effect of memantine. ISB remitted with the addition of memantine 20 mg daily after multiple failed trials of various psychotropics. Two years later, the reemergence of ISB resolved with memantine 25 mg, and was well tolerated with stable medical tests. Memantine could be a promising medication for the control of ISB in these patients when used as an adjunct. <h3>This research was funded by</h3> NA