Is there life after diagnostic death?

“I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description, and perhaps I could never succeed in intelligibly doing so. But I know it when I see it.”

- United States Supreme Court Justice Potter Stewart, on pornography, 378 U.S. 184 (1964)

For all the advances in knowledge about brain dysfunction and psychological suffering, clinicians and researchers still struggle over how best to define and package mental illness into neat categories. Classification systems for psychiatric disorders remain based entirely on phenomenology, with no pretense of implied etiology ever since publication of DSM-III. (Prior to DSM-III, it was known that all of mental illness resulted from unconscious conflict and bad parenting. Prior to those explanations, it had been known since antiquity that melancholia was caused by black bile while most other emotional problems resulted from wandering uteruses.) With each new DSM edition, expectations swelled that diagnostic classification would reflect greater knowledge about etiology, or at least pathophysiology. But with no real “eureka” moments about the causes of mental illness since Freud hit upon the Oedipal complex, hopes have been dashed time and time again as each revised diagnostic manual has done little more than reshuffle the same tired symptom card deck.

Dangling from the cliffhangers of yesteryear’s DSM or ICD, mental health professionals fervently await new revelations about the fundamental nature of mental illness. What cardinal symptoms will no longer be cardinal? For what ailments will age ranges become broadened, or narrowed? What new diagnoses will spring to life, and which old ones will be retired? Will two or more disorders that share a common outcome get subsumed as one? Will a time-honored condition (like Post-Traumatic Stress Disorder (PTSD) or Obsessive Compulsive Disorder (OCD)) secede from its greater symptom union and declare its diagnostic independence? And will any particular symptom(s) (e.g., non-suicidal self-injury) break free from their broader diagnostic symptom group and hit the road solo?

Neuroscientists, and patient advocacy groups, worry that without measurable laboratory correlates, the validity of mental illness falls subject to discreditation. Such concerns have somehow managed not to plague nonpsychiatric disorders that lack laboratory markers but remain solely “clinical” diagnoses - such as migraine, tinnitus, trigeminal neuralgia, or Parkinson’s Disease. Perhaps psychiatry has damaged its own credibility by constantly changing around disease state definitions (e.g., mixed bipolar states (Koukopoulos and Sani, 2014)), waffling over basic concepts across DSM editions (e.g., antidepressant-induced mania), and bickering over whether or not a disorder even exists (e.g., attenuated psychosis syndrome).

Decades ago, Robins and Guze (1970) suggested that “clinical description” was only one of several components relevant to making a psychiatric diagnosis, alongside follow-up studies, exclusion of other disorders, family history, and laboratory studies. The latter of these has increasingly become embraced to the near-exclusion of symptoms altogether, as reflected in alternative diagnostic systems such as NIMH’s RDoC - where no condition exists unless it maps to a known gene or circuit. Critics argue that dysfunctional neural pathways are no more diagnostically specific than symptom clusters, and forewarn that “signature” neural circuit patterns won’t likely help much to define categorical psychiatric diagnoses (Gillihan and Parens, 2011).

There is something scientifically disingenuous about taxonomy alternatively becoming a popularity contest, where diagnoses are inventions subjected to consensus opinion, rather than natural phenomena to be discovered. DSM has long been criticized because its diagnostic constructs are included only if they can be reliably agreed upon by clinicians - regardless of whether a given diagnosis is truly valid. Hence, mixed anxiety-depressive disorder failed to make the cut for DSM-5 not because depression plus anxiety seldom co-occur, but because DSM-5’s field trial raters couldn’t agree on its presence as a cohesive entity. Proposals to inaugurate “parental alienation syndrome” fell short of the mark not because the gene that causes it is epistatically suppressed by the gene for conduct disorder, but because of more successful lobbying efforts by its opponents than its proponents. Premenstrual dysphoric disorder emerged from the purgatory of DSM-IV’s appendix by dispensation some 15 years after an expertroundtable decided it was a disorder unto itself (Endicott et al., 1999). Severe Mood Dysregulation (SMD) and its variant Temper Dysregulation with Dysphoria (TDD) were both vetted unsuccessfully as possible diagnoses but it was Disruptive Mood Dysregulation Disorder (DMDD) - fortuitously discovered just before DSM-5’s publication - that ultimately spared rageful children from erroneous overdiagnoses of pediatric bipolar disorder (Holtmann et al., 2008). No one yet knows the fate of DMDD sufferers when their diagnoses expire upon their 18th birthday.

DSM-5 is replete with examples of once-clinically-relevant but now-obsolete entities, such as Asperger’s Syndrome, dysthymia, hypochondriasis, and all subtypes of schizophrenia - henceforth only to be seen but not heard, or coded. Had earlier drafts of DSM-5 prevailed, personality disorders in their entirety would have vanished from the clinical lexicon (if not from the clinic) in one fell swoop. How does a doctor tell a patient that their condition has no known cause and no longer exists, but still needs treatment?

So long as etiology remains a mystery, psychiatric differential diagnoses will likely remain an endeavor of sifting through shorthand categories that at best reflect reasoned conjecture, colored by prevailing cultural norms and lacking context or foundation. New or revised classification systems such as DSM-5, ICD-11 and RDoC may not do much to help us better define any psychiatric diagnosis, but to paraphrase US Supreme Court Justice Potter Stewart, we’ll likely still know it when we see it.