The occurrence of comorbidities with affective and anxiety disorders among older people with intellectual disability compared with the general population: a register study

BACKGROUND: Little is known regarding the burden of comorbidities among older people with intellectual disability (ID) who have affective and anxiety disorders. Therefore, we aimed to investigate the occurrence and risk of psychiatric and somatic comorbidities with affective and/or anxiety disorders in older people with ID compared to the general population. METHODS: This population study was based on three Swedish national registers over 11 years (2002–2012). The ID group was identified in the LSS register, which comprises of data on measures in accordance with the Act Concerning Support and Service for Persons with Certain Functional Impairments (n = 7936), and a same-sized reference cohort from the Total Population Register was matched by sex and year of birth. The study groups consisted of those with affective (n = 918) and anxiety (n = 825) disorder diagnoses. The information about diagnoses were collected from the National Patient Register based on ICD-10 codes. RESULTS: The rate of psychiatric comorbidities with affective and anxiety disorders was approximately 11 times higher for people with ID compared to the general reference group. The two most common psychiatric comorbidities occurred with affective and anxiety disorders were Unspecified non-organic psychosis and Other mental disorders due to brain damage and dysfunction and to physical disease (8% for each with affective disorders and 7 and 6% with anxiety disorders, respectively). In contrast, somatic comorbidity comparisons showed that the general reference group was 20% less likely than the ID cohort to have comorbid somatic diagnoses. The most commonly occurring somatic comorbidities were Injury, poisoning and certain other consequences of external causes (49 and 47% with affective and anxiety disorders, respectively) and Signs and symptoms and abnormal clinical and laboratory findings not elsewhere classified (44 and 50% with affective and anxiety disorders, respectively). CONCLUSION: Older people with ID and with affective and anxiety diagnoses are more likely to be diagnosed with psychiatric comorbidities that are unspecified, which reflects the difficulty of diagnosis, and there is a need for further research to understand this vulnerable group. The low occurrence rate of somatic diagnoses may be a result of those conditions being overshadowed by the high degree of psychiatric comorbidities.