What we’ve said about Comorbidity

The presence of one disorder does not exclude another. Many practitioners prize parsimony, but a patient with pneumonia can still have lung cancer, and the cancer may even be setting the stage for the pneumonia.

Weigh each possible diagnosis and find which ones are supported; there is no strict hierarchy. The hierarchy applies when mania, hypomania, acute psychosis or OCD are clearly present, since they impair your ability to elicit or observe the features of another condition.

The responsible psychiatrist identifies comorbidities even when they are subthreshold for a DSM diagnosis, tells the patient about them and recommends how to manage them.

When a patient carries many diagnoses, step back and think a little harder about what might be driving all of the symptoms. That does not necessarily mean it is just one illness. One old estimate is that maybe 80 percent of patients have a single form of psychopathology and 20 percent some comorbidity; it may not be based on research, but maybe it is a good rule of thumb.

Ask whether a personality disorder is driving the symptoms. Patients with borderline personality disorder frequently get diagnosed with multiple Axis I conditions that are often the result of the core borderline disorder: depression in the face of rejection or abandonment, anxiety in interpersonal situations, trouble sleeping because relationships are up and down.

Ask about family history too: a patient whose father, grandfather and uncle had bipolar illness, who is always cycling, anxious and sometimes cannot sleep because the mind is racing, may have a subsyndromal bipolar condition.

Labeling ADHD as the primary problem can tunnel you and the patient into a lifetime of escalating stimulants.

ADHD does not explain every aspect of a person. Do not use one diagnosis to account for trait after trait.

Patients now often arrive with four, five or six psychiatric diagnoses, which before DSM-III was exceptionally rare. DSM-III and especially DSM-III-R removed a lot of the hierarchy, making it possible to diagnose generalized anxiety disorder and major depressive disorder, or autism and ADHD, in the same patient.

Much of this, we believe, is spurious or false comorbidity, which a diagnostic hierarchy would help resolve. Long lists usually result in excessive polypharmacy and symptom-based descriptions, and inappropriate polypharmacy is rampant in patients with borderline personality disorder.

A list like bipolar disorder, MDD, ADHD, GAD and lupus leaves clinicians with no frame of reference for how to think through the problem or which medication to start. With the wrong or a heterogeneous set of diagnoses, the right treatment is not delivered in a timely fashion and people do not get better.