A Neurology and Psychiatry Merger: Quest for the Inevitable?

If a Martian with human-like anatomy and physiology visited Earth, how would humans explain why pulmonologists treat lungs, cardiologists treat hearts, and nephrologists treat kidneys, but neurologists treat some brain conditions and psychiatrists treat other brain conditions? That’s the question Thomas J. Reilly, BSc, MBChB, of the University of Glasgow in the United Kingdom, posed in a thought experiment published in the BJPsych Bulletin.¹

His point is plain: “It is difficult to rationally explain to someone with no prior frame of reference why we have the split between neurological and psychiatric illness.”

Neurology typically focuses on conditions with physical markers, such as neuropathological lesions, and psychiatry focuses on abnormal brain function determined through observable symptoms, Dr Reilly notes. However, he points out that epilepsy fell under the purview of psychiatrists until its neuropathology became clear and neurologists began treating it. Magnetic resonance imaging (MRI) and other tests are similarly starting to reveal potential biomarkers for schizophrenia and autism.

Trying to delineate the disciplines with different symptomology falls flat, too. Recently identified N-methyl-D-aspartate receptor encephalitis is “clinically indistinguishable from the first episode of schizophrenia” despite having a clear neurologic pathophysiology, Dr Reilly writes. Some symptoms overlap, such as hallucinations in psychosis and Parkinson disease, depression in mood disorders and multiple sclerosis, or a variety of symptoms in different types of dementia.

“Current classification is based on convention, tradition, and quirks of history,” Dr Reilly writes. “Nature does not respect our arbitrary categorizations and neither do our patients.”

Dr Reilly is not alone in his thoughts. Since his editorial was published in 2015, several more articles have similarly questioned the division and proposed either merging the 2 specialties or at least designing a curriculum for a third path that brings them together in neuropsychiatry or behavioral neurology.² Although such joint programs exist throughout the world, including in the United States, they are far from the standard.

Historical Underpinnings and Global Variation

Historically, a single discipline, neuropsychiatry, dominated study and care of brain disease, particularly in the 19th century. However, neurology and psychiatry began to diverge gradually around the 1930s or, especially after the 1960s, depending on who you talk to and what country you’re talking about.^3,4

Glen Elliott, PhD, MD, chief psychiatrist and medical director of Children’s Health Council in Palo Alto, California, puts the beginning of the split even earlier, largely as a result of the influence of Freud’s theories at the end of the 19th century.

“Neurology has always been solidly in the ‘real medicine’ field, whereas psychiatrists, particularly when we were heavily into psychoanalysis,” became more distant from the rest of medicine, Dr Elliott told Neurology Advisor. “That rift has gradually begun to heal as both neurologists and psychiatrists have acquired a broader array of effective interventions and as conceptualizations about psychiatric illnesses have focused more on brain dysfunction rather than on upbringing.”

Family influences still play a major role in psychiatry, he said, particularly in his field of child psychiatry, where helping parents make certain changes to their parenting methods can be crucial to effective treatment. “But that’s not the way neurologists tend to think,” he said.

For the most part, the fields have distinct approaches, philosophies, research principles, and treatment methods to nervous system disorders.³ Psychiatrists, for example, “favored symptom descriptions over laboratory tests,” writes Agustín Ibáñez, PhD, of Favaloro University’s Institute of Cognitive and Translational Neuroscience in Buenos Aires, Argentina, and colleagues.³

Dr Elliott would agree. Neurologists seek identifiable pathology by methods such as computed tomography scans, MRI, electroencephalography, magnetic encephalograms, and other more objective tests, he said, whereas psychiatrists lack useful biomarker tests for psychiatric disorders.

“Even the neurological examination is much more precisely symptom oriented, whereas the psychiatry examination is more about mental status,” Dr Elliott said. “Neurologists have all sorts of lovely physical signs that help them locate what part of the brain might be affected and what level of the nervous system may be involved.”

In some ways, the difference between a neurologic vs a psychiatric condition is how concrete or nebulous its diagnosis is.

“Psychiatry tends to be responsible for disorders where they markedly affect behavior but there’s no clear way of identifying what’s causing it except clinical interview,” Dr Elliott told Neurology Advisor.

Historical examples, such as Dr Reilly’s epilepsy example, bear this out. When Dr Elliott was in medical school, Parkinson disease was largely considered a psychiatric disorder — until physicians had specific treatments for it and a reasonable hypothesis about its underlying mechanism. It’s not just neurology that gets disorders previously under psychiatry’s domain: the psychosis caused by tertiary syphilis was a major reason for psychiatric institutionalization until its cause was recognized as a treatable infectious disease.

“It no longer was a psychiatric issue because we had a defined cause and a specific treatment,” Dr Elliott said. Similar examples include sleep disorders such as narcolepsy and sleep apnea, which now fall under neurology or otolaryngology.

The distinctions between neurology and psychiatry vary considerably across the world, Dr Elliott notes. Italy has largely included psychiatry under neurology’s umbrella, he said. Dr Reilly, from the United Kingdom, notes in his review that conversion disorder, with its neurologically unexplained symptoms, has no neuropathologic explanation, yet is treated by neurologists.5 In the United States, however, Dr Elliott said patients with conversion disorder are referred to psychiatrists as soon as the diagnosis is made.

The United States already recognizes the overall link between the fields institutionally: board examinations are managed by the American Board of Psychiatry and Neurology. Although neurology and psychiatry board examinations remain distinct, a few of the subspecialties overlap the two.

Inevitably Separate or Inevitably Merged?

The fields’ differences tend to loom larger than their similarities for many who weigh in on this issue, however.

“The skill sets are very different,” Dr Elliott told Neurology Advisor. “Yes, in theory overlapping them makes a lot of sense, but very different types of people get pulled to the two.” Except where medication is involved, “the psychiatric approach to diagnosis and treatment is quite different from the neurology approach,” he said. Bridging such a gap likely also means sacrificing something from both because only so much time exists for training, and neurology and psychiatry already each comprise major components of schools’ core curricula, he said.

Some, such as Dr Reilly, see so little distinction that they insist a single discipline is ideal. Others take a more measured approach, such as Carole Azuar and Richard Levy, MD, PhD, both in the department of neurology at Pitié-Salpêtrière Hospital in Paris, France.⁴ They argue that the advances of neuroscience have made it important at least to get the 2 disciplines talking more to one another.

“The behavioral symptoms that lie along the borders of both neurology and psychiatry by their expression and their underlying diseases have remained in the ‘blind spots’ of both disciplines,” they write. Patients with disorders whose symptoms may fall under neurology and psychiatry are often neglected, shuttled only toward one specialist, or receive disjointed care without discussion between their neurologist and psychiatrist. That occurs despite the recognition that behavioral disorders in general often arise from a combination of brain dysfunction and genetic, sensory, somatic, and/or environmental factors.

“The patients that are really hurt are the ones that fall between the cracks because we’re not sure what’s going on, and that happens in both disciplines,” Dr Elliott agreed.

The resulting knowledge gap has led to poor clinical characterization, limited care, inadequate knowledge about pathophysiology, and lack of teaching about these disorders, Ms Azuar and Dr Levy write. Yet clinical neuroscience can help “neurologists and psychiatrists to again speak a common language so that, together, they can now address the pathology of neuropsychiatric disorders.”

Bringing neurology and psychiatry together may also begin to address the “reproducibility crisis” that has plagued behavioral science particularly in recent years.⁶ Although many factors likely contribute to replication problems, “inadequate validation of laboratory-specific testing conditions” is a common cause, particularly in behavioral research, suggests Anne M. Andrews, PhD, and her colleagues at the University of California at Los Angeles.⁷ The use of rigorous, specific criteria and validation techniques that Andrews et al recommend would bring behavioral and psychiatric research closer to the objectivity seen in neurology research (although Andrews et al and others note that all disciplines could benefit from greater rigor).

Indeed, “we may be forced to come together in ways we wouldn’t have before,” Dr Elliott said, as a result of advances in psychiatric biomarkers and brain-region treatments. He noted that psychiatry has led the way with transcranial magnetic stimulation, but neurologists excel more at understanding the anatomy of the brain, a necessary skill for such treatments. He still expects conditions such as schizophrenia and autism, where MRI has begun to elucidate mechanisms, to require psychiatrists because they are trained to help families and patients manage behavioral issues that neurologists usually avoid.

Even still, some conditions blend the fields anyway, such as dementias. Neurologists tend to document the type of dementia and treat its progression whereas geriatric psychiatrists manage comorbid conditions and family systems issues, Dr Elliott said.

Perhaps it is that tension between undeniable differences and inevitable merging that has led to more recent calls for cross-disciplinary cooperation.

Making Synergy Happen

Dr Reilly does not propose a specific way to merge the disciplines, but several others have. Ms Azuar and Dr Levy focus on apathy and agitation/aggression as models for describing behavioral disorders and present 2 case studies that illustrate the need for synergy between neurology and psychiatry to reach accurate diagnoses.

Ibáñez et al suggest a neuropsychiatric approach to triangulate social neuroscience with neurology and psychiatry to better understand the “impaired social brain.”³ They discuss key domains of social neuroscience — facial emotion recognition, empathy, theory of mind, moral cognition, and ecologic assessment of social context — and note that disturbances in various neural networks lead to social cognition deficits in both neurologic and psychiatric disorders. Essentially, they argue that synergy among all 3 of these fields is necessary to fully understand and treat conditions involving social deficits.

Ibáñez et al acknowledge the hurdles in such a path, particularly in terms of the hyperspecialization that dominates clinical care, research funding, and academic programs. “A systematic triangulation can only become concrete if major educational and political changes are progressively made,” they write. “Even if shared social cognition impairments in neurological and psychiatric disorders are already broadly acknowledged, implementing this conception at an institutional level will constitute a major challenge.”³

Some US institutions already have neuropsychiatric units or have similarly combined neurology and psychiatry, such as the pediatric clinic at Stanford led by Lawrence Fung, MD, PhD, Dr Elliott said. However, academic politics and power issues are likely to complicate many such attempts, as are continued disparities in reimbursement for neurologic interventions compared with psychiatric ones, Dr Elliott added.

“When you’re talking about ‘coming together,’ it becomes a matter of whether it’s a merging of equals or of one profession getting swallowed up by another,” he told Neurology Advisor. “That’s the fear that keeps the 2 fields apart. If you have a combined department that was headed by a psychiatrist or neurologist, you might find that it’s not an equal distribution of resources in terms of what’s valued and what’s not.”

Perminder Sachdev, MD, PhD, FRANZCP, and Adith Mohan, MRCPsych, FRANZCP, of the University of South Wales and The Prince of Wales Hospital in Sydney, Australia, have taken a step toward tackling such a challenge by creating a third option in their “International Curriculum for Neuropsychiatry and Behavioral Neurology.”² They don’t propose a complete merging of the fields but rather an advanced curriculum of neuropsychiatry grounded in a firm education of both neurology and psychiatry. They acknowledge differences between the fields that Dr Reilly dismisses or overlooks and emphasize the need for a third specialty encompassing skill sets and approaches from both.

“Psychiatry prides itself in its rich phenomenological descriptions, nuanced observation of behavior, highly sophisticated interviewing skills, interpersonal sensitivity, ability to deal with ambiguity, and the seamless synthesis of the biological with the psychological,” and “only an exclusive training in psychiatry can deliver competence of all this,” Drs Sachdev and Mohan write. “Neurology lays claim to its unabashed empiricism, rigorous clinical examination skills, and its pure objectivity, again requiring considerable exposure and training in the traditional subject matter.”²

Hence, they have mapped out an extensive framework — including the territory, objectives, skills, competencies, and training — for a curriculum in neuropsychiatry, which is functionally indistinguishable from behavioral neurology, they note.

However it occurs, greater interaction between the 2 fields does seem inevitable, Dr Elliott says. The way it plays out, both in the United States and globally, will likely depend as much on cultural factors as on advancements in technology and understanding of the brain.

References

1. Reilly TJ. The neurology-psychiatry divide: a thought experiment. BJPsych Bull. 2015;39(3):134-135.
2. Sachdev P, Mohan A. An international curriculum for neuropsychiatry and behavioural neurology. Rev Colomb Psiquiatr. 2017;46 Suppl 1:18-27.
3. Ibáñez A, García AM, Esteves S, et al. Social neuroscience: undoing the schism between neurology and psychiatry. Soc Neurosci. 2018;13(1):1-39.
4. Azuar C, Levy R. Behavioral disorders: The ‘blind spot’ of neurology and psychiatry. Rev Neurol (Paris).2018;174(4):182-189.
5. US National Library of Medicine. Conversion Disorder. Medline Plus.https://medlineplus.gov/ency/article/000954.htm. Updated January 28, 2019. Accessed February 5, 2019.
6. Nosek BA, Cohoon J, Kidwell MC, Spies JR. Estimating the Reproducibility of Psychological Science. Open Science Collaboration. https://osf.io/ezum7/. Updated September 18, 2018. Accessed February 5, 2019.
7. Andrews AM, Cheng X, Altieri SC, Yang H. Bad behavior: improving reproducibility in behavior testing. ACS Chem Neurosci. 2018;9(8):1904-1906.