Differential Diagnosis vs Comorbid (Co-existing) Disorders

What other disorders should we consider?

There are specific psychiatric disorders that seem to have significant rates of comorbidity. In Dr. Biederman’s study, generalized anxiety disorder occurred in 20-36% of the ADHD adults, multiple anxiety disorders 42%, clinical depression (Major Depression) 30%, Bipolar Disorder 10%, alcohol/drug abuse 36-21%, social phobia 33-27%, antisocial personality disorder 18-10%. These percentages are conservative compared to other studies reporting higher comorbid rates. Other studies have reported mood disorder comorbidity occurring up to 57%. These high rates of comorbidity were also found by Shekim et al. (1990). It's been reported that up to 70% of adults with ADHD have a second comorbid psychiatric disorder. In children, longitudinal studies with ADHD have reported increased risk for mood or anxiety disorders.

Therefore, the evaluation of the adult complaining of ADHD symptoms requires the consideration of additional psychiatric conditions.  Focusing solely on ADHD symptoms may obscure the need to treat other co-existing conditions before treating ADHD.  The goal of treatment is to improve one condition without worsen others.  The premature prescription of medication for ADHD may worsen the symptoms of a co-existing condition. For example, stimulant medication can increase panic and obsesssive-complusive symptoms. Understanding this approach is critical to quick and effective treatment.

If several disorders exist together, which disorder do we treat first?

This is an excellent question and one that has only recently been answered by published research. As mentioned earlier, a misdiagnosis or the presence of an unrecognized psychiatric disorder may lead to treatment that is ineffective or, worse, harmful. In a personal communication to me, Drs. Biederman and Wilens at Harvard suggest that any mood disorder be stabilized first before the stimulant treatment of ADHD. As an expert in mood disorders, this has been my mode of treatment for several years.  Presently, the recommended sequence of treatment for comorbid disorders in the presence of ADHD is the following: Alcohol and substance use disorders first, followed by stabilizing mood disorders ( Bipolar Disorder and Major Depression), then anxiety disorders (Panic, Generalized Anxiety Disorder, Obsessive-Compulsive Disorder), and finally ADHD. This algorithm, applied to ADHD, is the diagnostic algorithm found the DSM-IV (the manual for psychiatric diagnoses published by the American Psychiatric Association) for diagnosing co-existing symptoms.

It is essential that all existing psychiatric conditions be accurately identified, then prioritized for treatment so that a thoughtful sequence of medication trials can be instituted. Because the first medication trial may not be successful, it is necessary for the physician to document any partial response and notable side effects occurring with each medication. This allows for the accumulation of data that will increase the likelihood of finding the right medication. When comorbid disorders exist, medication combinations may be necessary. The combination may be more effective than a single medication.

The diagnosis of adult attention deficit hyperactivity disorder is very complex. The clinician needs to consider differential diagnoses before reaching a diagnostic conclusion. Then the presence of comorbid conditions needs to be reviewed by asking specific questions. Only after a comprehensive evaluation is completed can the issues of medication be considered. Research on treatment algorithms is still in its infancy. The continuing emergence of research findings and the refinement of the clinical skills of health professionals will improve the accuracy of diagnoses and treatment.