Psychotic Disorder Due to Another Medical Condition 117 been estimated to range from 0.21% to 0.54%. When the prevalence findings are stratified by age group, individuals older than 65 years have a significantly greater prevalence of 0.74% compared with those in younger age groups. Rates of psychosis also vary according to the underlying medical condition; conditions most commonly associated with psy- chosis include untreated endocrine and metabolic disorders, autoimmune disorders (e.g., systemic lupus erythematosus, N—methyl—D—aspartate (NMDA) receptor autoimmune en- cephalitis), or temporal lobe epilepsy. Psychosis due to epilepsy has been further differ— entiated into ictal, postictal, and interictal psychosis. The most common of these is postictal psychosis, observed in 2%—7.8% of epilepsy patients. Among older individuals, there may be a higher prevalence of the disorder in females, although additional gender-related fea- tures are not clear and vary considerably with the gender distributions of the underlying medical conditions.
Psychotic disorder due to another medical condition may be a single transient state or it may be recurrent, cycling with exacerbations and remissions of the underlying medical condition. Although treatment of the underlying medical condition often results in a res- olution of the psychosis, this is not always the case, and psychotic symptoms may persist long after the medical event (e.g., psychotic disorder due to focal brain injury). In the con- text of chronic conditions such as multiple sclerosis or chronic interictal psychosis of epi- lepsy, the psychosis may assume a long-term course.
The expression of psychotic disorder due to another medical condition does not differ substantially in phenomenology depending on age at occurrence. However, older age groups have a higher prevalence of the disorder, which is most likely due to the increasing medical burden associated with advanced age and the cumulative effects of deleterious exposures and age-related processes (e.g., atherosclerosis). The nature of the underlying medical conditions is likely to change across the lifespan, with younger age groups more affected by epilepsy, head trauma, autoimmune, and neoplastic diseases of early to mid- life, and older age groups more affected by stroke disease, anoxic events, and multiple sys- tem comorbidities. Underlying factors with increasing age, such as preexisting cognitive impairment as well as vision and hearing impairments, may incur a greater risk for psy- chosis, possibly by serving to lower the threshold for experiencing psychosis.
Course modifiers. Identification and treatment of the underlying medical condition has the greatest impact on course, although preexisting central nervous system injury may confer a worse course outcome (e.g., head trauma, cerebrovascular disease).
The diagnosis of psychotic disorder due to another medical condition depends on the clin- ical condition of each individual, and the diagnostic tests will vary according to that con- dition. A variety of medical conditions may cause psychotic symptoms. These include neurological conditions (e.g., neoplasms, cerebrovascular disease, Huntington‘s disease, multiple sclerosis, epilepsy, auditory or visual nerve injury or impairment, deafness, migraine, central nervous system infections), endocrine conditions (e.g., hyper- and hypo- thyroidism, hyper- and hypoparathyroidism, hyper- and hypoadrenocorticism), metabolic conditions (e.g., hypoxia, hypercarbia, hypoglycemia), ﬂuid or electrolyte imbalances, hepatic or renal diseases, and autoimmune disorders with central nervous system involve- ment (e.g., systemic lupus erythematosus). The associated physical examination findings, laboratory findings, and patterns of prevalence or onset reﬂect the etiological medical condition.
Suicide risk in the context of psychotic disorder due to another medical condition is not clearly delineated, although certain conditions such as epilepsy and multiple sclerosis are associated with increased rates of suicide, which may be further increased in the presence of psychosis.