In the present study, we found small differences in adult outcome between individuals with AD and individuals with PDD NOS. The overall adult outcome in both AD and PDD NOS groups was poor, with excessively increased disability rates in both groups relative to the general population, and with almost all individuals being unmarried at follow-up. There were no elevated mortality or conviction rates in either group. Disability pension award was the only outcome measure that differed between the diagnostic subgroups, and that was explained by difference in psychosocial functioning (CGAS) rather than by diagnostic category.
Disability Pension Award and Marital Status
Eighty-three percent of the individuals in this study received disability pension awards, and 95% were unmarried at follow-up. This is consistent with previous studies showing poor prognosis in ASD individuals (Billstedt et al. 2005
; Gillberg and Steffenburg 1987
; Cederlund et al. 2007
; Hofvander et al. 2009
; Howlin et al. 2000
; von Knorring and Hagglof 1993
). In our study, 35% of the ASD individuals were diagnosed with PDD NOS. Despite a lower symptom load in this group, we found a markedly elevated rate of disability pension awards, and a substantial majority was unmarried also in this group. Our findings are in line with two previous studies that reported similar severe handicaps in adults with PDD NOS/autistic-like conditions, in which few individuals were living normal social lives and functioning well at work (Billstedt et al. 2005
; Hofvander et al. 2009
). Hofvander et al. reported a somewhat better prognosis for their participants than for ours or Billstedt’s, but this is probably attributable to the normal-range intellectual level of their individuals. In our study, 33% of the patients were in the upper intellectual range compared with only 18% in the Billstedt study, but the prognosis was similar, with a poor outcome in almost 80% of the cases in both studies. However, comparisons must only be tentative. In our study, outcome was based on marital status, disability pension award, mortality and convictions as measures for prognosis. Billstedt et al. used the more graded outcome criteria published by Lotter (Lotter 1974
Predictors of Disability Pension Award
Childhood intellectual level and language function before age 6 years have been reported to be the most important predictors of outcome in ASD individuals (Baghdadli et al. 2007
; Billstedt et al. 2005
; Howlin et al. 2004
; Kobayashi et al. 1992
; Szatmari et al. 2003
). In the present study, disability pension award was the outcome measure providing most information about adult outcome. Interestingly, our results indicated that low psychosocial function (CGAS) at admission seemed to be more associated with disability pension award at follow-up than intellectual level. These factors are obviously interacting, but the results suggest that assessment of CGAS, in addition to intellectual level, provide useful information about outcome. Because CGAS is a global measure, it also measures adaptive capacity, which is one of the most impaired functions in individuals with ASD. Thus, this instrument may capture important information relevant to prognosis that intellectual level as a prognostic factor may miss. In ASD populations known to be difficult to test and where precise IQ scores may be unreliable, assessing CGAS may be especially useful. However, few previous studies have used CGAS as a predictor of outcome (DeMaso et al. 1995
; Gold et al. 1993
; Sourander et al. 1996
), and less research has been conducted on the measurement of functional impairment than on psychiatric disorders (Szatmari 2009
). Szatmari and colleagues (Szatmari et al. 2002
) have claimed that the severity of symptoms and level of functioning are two phenotypic dimensions that do not always correlate. CGAS incorporates both these dimensions in one global assessment and could therefore be useful as an additional tool when estimating outcome in individuals with ASD.
We found that AD was no more associated with disability pension award than was PDD NOS when we adjusted for intellectual level and CGAS. This is in line with research conducted by Billstedt et al. (2005
), in which AD and other ASD subgroups with similar intellectual levels were equally predictive of a poor outcome. Because our findings indicate that outcome seem to depend more on level of functioning than degree of autistic symptoms, our findings support a dimensional model of ASD as proposed in the DSM-V revision (American Psychiatric Association 2010
Previous research has paid little attention to whether contextual variables predict later outcome in ASD individuals (Seltzer et al. 2004
). We found no association between chronic family difficulties and subsequent disability pension at follow-up, nor did we find any gender differences. This is consistent with Howlin’s findings (1997), who reported that the effects of family factors and gender were unclear. However, mapping contextual factors that promote or impede development in ASD individuals should be emphasized in future research. The prevalence of ASD has increased markedly within the last decades (Fombonne 2005
), and many people will need the support of their families and society in the future. With regard to gender, reported studies have often suffered from small female samples (Billstedt et al. 2005
; Gillberg and Steffenburg 1987
; Howlin 1997
; Piven et al. 1996
), and future research must use larger female populations to draw conclusions about gender differences.
Only seven individuals in our ASD population were convicted of crimes. The low conviction rate is in line with the results of Mouridsen et al. (2007
), who found that former child psychiatric inpatients with ASD had about half the conviction rate of a matched control group. However, five out of seven convicted patients in our sample belonged to the PDD NOS group, and recent studies have found that there are differences in criminal behavior between subgroups of people with ASD (Mouridsen et al. 2007
; Siponmaa et al. 2001
). The tentative, but not statistically significant, difference we found in our study may have been caused by the different intellectual and functional levels between the groups, but a definitive answer awaits future research on larger populations.
The mortality rate among males (2%) in our study must be regarded with caution because of the small numbers, but it did not seem to be high in either the AD group or the PDD NOS group. Previous research has found that persons with ASD tend to have an increased mortality risk (Gillberg et al. 2010
; Mouridsen et al. 2008
; Shavelle et al. 2001
), regardless of ASD subtypes (Gillberg et al. 2010
). However, research on mortality in ASD populations is limited, and the representativeness of study populations has been unclear. In our study, only 14% of the individuals had a comorbid organic brain disorder at baseline, which contrasts with a study by Gillberg et al. (2010
) in which a large proportion of the participants had additional specific medical disorders.
With one female (4%) from a small female population registered dead at follow-up, we cannot conclude anything about female mortality, but our findings do not contradict recent research in which female gender were associated with an increased risk of early death (Mouridsen et al. 2008
; Shavelle et al. 2001
Strengths and Limitations
The present study has several strengths. We have examined a large group of patients. It is a nation-wide study, and no regional admission bias should be in force. The follow-up period is long relative to that used in most other studies. Rediagnosis and scoring of the study population was completed before the outcome information was collected, and thus scoring was performed blind to outcome. The reliance on four experienced clinicians (one expert in the field of autism) to make consensus best-estimate diagnoses ensured that the diagnosis of PDD NOS was applied as accurately as possible. The outcomes are based on high-quality national registers.
The present study also has some general limitations that must be considered when interpreting the results. Follow-up studies of clinical samples will always have problems with representativeness of such samples. This study is based on inpatient admissions only, and the study population may not be representative of child psychiatric patients in general. However, the NCCAP was a national institution and patients were referred from all over Norway. During the period we examined, fewer children were seen at local clinics and individuals with suspected pervasive developmental disorders were often admitted as inpatients. These factors make our population less selective than would have been the case today. Because our ASD population was identified by chart review, according to current DSM-IV criteria, and not upon the criteria at the time of admission, we also ensured that children representing the broader spectrum of autism disorders than strictly defined AD were included.
All information was based on chart review from hospital records, which are not reliable scientific sources of information in all aspects. File-based information should always be interpreted with caution. However, the hospital records were of good quality, giving a detailed and thorough description of the patients’ symptoms and behavior, psychometric test results and family functioning. All the records were read independently by at least two clinicians, and the rediagnosis and scoring of the data were completed by experienced psychiatrists. We conducted an extensive interrater reliability study, and the interrater reliability was high for the diagnoses. This is consistent with previous research in which validity of file-based diagnostic ratings has been satisfactory (Grann et al. 1998
; McKenzie et al. 2011
Unfortunately, standardized IQ instruments were not systematically used during hospitalization. To mitigate this problem, we reassessed the cognitive level according to DSM-IV criteria for level of mental retardation. The interrater reliability for the cognitive level assessments was very good, reflecting the detailed information about cognitive attainment in the records.
We also found the CGAS and CFD scale scores to be reasonably reliable between raters, in line with previous research (Aasland et al. 1997
; Bird et al. 1987
; Flato et al. 1997
). The detailed medical histories in the hospital records largely compensated for the lack of direct observations of the children and their families.
The outcome measures were derived from register data, and prognosis was based on disability pension award, marital status, convictions and mortality. We did not use the Lotter (1974
) outcome criteria (“good”, “fair”, “restricted” and “poor”) that are most often used in other studies, so comparisons must be done with caution and prognoses should only be tentative. The outcome measures we used, however, were robust official register data, and they were not influenced by the investigators.
Factors identified in this study are probably not causative factors, but rather they are markers of vulnerability factors that increase the risk of disability pension award within an ASD population, and they should be interpreted as such.
Finally, if the proposed DSM-V criteria are accepted, this study compares outcome differences in diagnostic groups that would no longer exist. However, we believe our study still adds information about the long-term outcome of ASD individuals, while supporting the future dimensional approach.