In adult patients with obsessive-compulsive disorder who are thought to have comorbid attention-deficit/hyperactivity disorder, the symptoms of inattention, forgetfulness, and impaired executive function might actually be an epiphenomenon of OCD rather than a manifestation of ADHD, a study has shown.
OCD patients’ "continuous and excessive attempts to control behavior and thoughts" may cause a flooding of the executive system, interfering with attention, memory, and other executive processes, said Amitai Abramovitch, Ph.D., of the department of psychiatry, Harvard Medical School, Boston, and his associates.
"We believe that there is a growing convergence of evidence that may, at least in some cases, challenge the diagnostic validity of OCD and ADHD comorbidity." Making a clear distinction between the two disorders is crucial because stimulant medication given to treat ADHD is known to exacerbate OCD symptoms and has even been reported to induce full-blown OCD, the researchers noted in the second of two papers they have written on the topic (J. Obsessive Compuls. Relat. Disord. 2013;2:53-61).
Dr. Abramovitch and his colleagues began with the observation that OCD and ADHD have very different, even directly opposite, clinical presentations. ADHD is characterized primarily by impulsivity, risk taking, and novelty-seeking behavior. "In contrast, the behavioral manifestations of OCD seem to lie on the opposite end of an impulsive-compulsive spectrum," typified by inhibited temperament, avoidance of novel stimuli, increased risk avoidance, and lower than normal impulsivity.
In addition, the hallmark of OCD is performance of repetitive, precise, and accurately timed rituals, which requires extremely focused attention. "It seems highly unlikely that individuals with ADHD would be able to perform such precise and repetitive rituals," wrote Dr. Abramovitch, also with the department of psychiatry, OCD and related disorders program, at Massachusetts General Hospital, Boston.
Another distinction is that ADHD presents early in childhood, while the average age of onset for OCD is 19 years.
Physiologically, both disorders are characterized by abnormal frontostriatal activity, which until now might have been mistaken as a similarity between the two. But the pattern of this activity is very different.
OCD is associated with increased metabolic activity in certain areas of the frontostriatal network such as the orbitofrontal cortex, thalamus, and caudate nucleus, during resting state, performance on some neuropsychological tasks, and under symptom provocation conditions. This is thought to reflect "executive hypercontrol and a preference toward controlled information processing." In contrast, ADHD is associated with frontostriatal hypoactivity during resting state and provocation.
To test their hypothesis that OCD and ADHD are so fundamentally different that they’re unlikely to coexist in the same person, the researchers assessed 30 men with OCD, 30 men with ADHD, and 30 healthy control subjects who had no history of psychiatric, neurologic, developmental, or learning abnormalities. The three groups were well matched for age (mean, approximately 30 years) and level of education (mean, approximately 13 years) (J. Neuropsychology 2012;6:161-91).
All the subjects in the OCD and ADHD groups had their diagnoses validated using the Mini International Neuropsychiatric Interview (MINI), and the absence of mental disorders was verified in the control subjects using the same instrument. All the subjects completed a short computerized battery of neuropsychological tests, personal interviews, and assessments using the Eysenck Impulsiveness-Venturesomeness-Empathy (IVE) scale, an ADHD questionnaire based on DSM-IV criteria, and the Obsessive-Compulsive Inventory-Revised (OCI-R).
The ADHD group scored significantly higher on measures of impulsiveness than both the OCD group and the control subjects. Scores in the latter two groups were similar to each other. In contrast, the OCD group achieved significantly higher scores on the OCI-R than both the ADHD group and the control subjects. However, both the ADHD and OCD groups performed worse than controls on neuropsychological measures.
The ADHD and OCD groups also were significantly different from each other in an assessment of longitudinal behavioral traits from childhood through the present day. The subjects with ADHD showed continuity of inattention, impulsivity, and hyperactivity throughout their life spans.
In contrast, almost all the subjects with OCD reported that they never had symptoms during childhood similar to their current symptoms in adulthood. Only the five subjects with the most severe OCD reported such continuity of symptoms throughout their life spans.
These same five men with OCD scored high on inattention items on the ADHD questionnaire, but not on impulsivity or other items. This suggests that their inattention, which could mistakenly be interpreted as representing ADHD, was actually an epiphenomenon of executive impairment from the OCD, Dr. Abramovitch and his associates said.
"Our model may contribute to clinicians as well as individuals diagnosed with OCD in proposing that neuropsychological impairments may be viewed as a second-order consequence of OC symptoms," they wrote.