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Brain Trust

No Laughing Matter

Marcolini, Evie, MD

doi: 10.1097/01.EEM.0000554843.16626.01
Brain Trust

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We called a senior resident where I trained the pathological smiler. Through no fault of his own, he was always smiling. I mean always. He couldn't help it, even when he was delivering bad news to a family. Little did I know at the time that there was such a thing as pathological laughter. It's good that I didn't because I was aggressively diagnosing everything in myself and my friends regardless of evidence in my early education, the so-called second-year syndrome.

Our senior resident did not have this, but there is an entity called pathological laughing and crying (PLC), which is part of an involuntary emotional expression disorder. The two classifications of this disorder are different because PLC is uncontrollable and not linked to any appropriate trigger, while emotional lability (EL) is typically associated with mood disorders and is usually an exaggerated response to a related trigger. (BMC Neurol 2015;15:196; http://bit.ly/2thdRHg.)

Don't start self-diagnosing based on the last time you found yourself crying at the drop of a hat. These are true neurologic entities. In fact, a rare form of PLC called fou rire prodromique, which translates to a prodrome of crazy laughter, was described as early as 1903 as a precursor to stroke. (Rev Neurol [Paris] 1903;7:353.) These transient attacks of laughter have been described to last from a few seconds to 30 minutes, and have been associated with ischemic and hemorrhagic stroke of the internal capsule, lenticular nucleus, thalamus, and brainstem. (J Emerg Med 2018;55[5]:707.)

The patient with PLC has episodes of uncontrollable laughter, crying, or both that are typically associated with four clinical scenarios. The first is with gelastic (laughing) or dacrystic (crying) seizures, which are focal seizures often caused by a congenital lesion (hamartoma) on the hypothalamus. Hypothalamic hamartoma is rare, affecting one in 200,000 children, and difficult to diagnose because the clinical manifestation of the seizure is focal with uncontrollable laughing or crying. (Ultrasonography 2016;35[4]:353; http://bit.ly/2tlhHiJ.) You can see how this would be challenging to figure out in a young child. It is also associated with pseudobulbar palsy and subcortical and brainstem infarctions and tumors.

PLC has been associated with stroke, traumatic brain injury, multiple sclerosis, amyotrophic lateral sclerosis, brain tumor, central pontine myelinolysis, Parkinson's disease, and cerebellar atrophy. Neuroimaging was not available when fou rire prodromique was first described, and neurologic diseases were diagnosed by autopsy, making the diagnosis and pathology challenging.

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A Medical Mystery

The pathophysiology of PLC has been a bit of a mystery for many years, and is still not completely worked out. Since the advent of advanced neuroimaging, PLC has been associated with ischemic lesions in the frontal lobe, cerebral hemispheres, thalamus, brainstem, and cerebellum. This makes sense considering the complexity of laughing.

Laughing may seem easy, but it is a complex function involving three anatomic areas. The cortex controls and modifies emotional responses to a stimulus, the bulbar nuclei trigger the facial expressions, and the hypothalamus integrates these two areas. Some describe this physiology with respect to two pathways: the hypothalamus-limbic system, which produces emotions, and the thalamocortical system, which controls expression. (Ann Emerg Med 1990;19[3]:327.)

Based on this description, pathological laughter can be caused by a disinhibition of the hypothalamus-limbic system or excessive stimulation of the thalamocortical system, both causing an exaggerated response. These cases are rare, and the definitive pathophysiology is elusive. Some implicate ephaptic transmission, which refers to neurons sending signals through axon-to-axon transmission, without utilizing typical neurotransmitter pathways. (J Neurol Neurosurg Psychiatry 2001;71[6]:802.)

It is important for emergency physicians to be aware of these rare diseases so they don't write off pathological laughter to a psychiatric or behavioral etiology and do make sure that brainstem stroke is in the differential. The time to think of it is when a patient exhibits bursts of laughter without an appropriate stimulus. The usual workup for altered mental status is appropriate, and stroke, although rare, should be considered.

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Dr. Marcoliniis an assistant professor of surgery and neurology, the director of critical care education in emergency medicine, and the fellowship director of neurocritical care at the University of Vermont Medical Center. She is also a member of the board of directors for the American Academy of Emergency Medicine. Follow her on Twitter @eviemarcolini. Read her past columns athttp://bit.ly/EMN-BrainTrust.

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