Differential Diagnosis: Tic Disorders vs Myoclonic Epilepsy

Though juvenile myoclonic epilepsy (JME) is the most common form of idiopathic generalized epilepsy, it is frequently misdiagnosed or overlooked. Such mistakes can result in inappropriate or even harmful treatment for this otherwise highly treatable disease.¹ Fortunately, the differential diagnosis is generally simple and straightforward.

The jerking movements associated with myoclonic epilepsy may be mistaken for tics, which are estimated to occur in 20% of children.² Tics can involve movements or vocal sounds and fall into 2 distinct categories: Simple tics are brief and typically involve only one muscle group – for example, eye blinking, head-jerking, or shoulder-shrugging. Complex tics involve more than one muscle group and may present as a sequence of paired behaviors like vigorously clearing the throat and then doing a specific hand motion each time the tic occurs.

“Because tics are so common, of course they will co-exist in some patients with epilepsy,” Nitin K Sethi, MD, MBBS, FAAN, an assistant professor of neurology at New York-Presbyterian Hospital/Weill Cornell Medical Center, told Neurology Advisor. However, despite 2 recently published population-based studies that reported surprisingly high rates of comorbid Tourette’s syndrome and other tic disorders in children with epilepsy, it is unlikely that these conditions actually co-occur at a higher rate than usual.^3,4

“From about 26 years of experience, I’d have to say that I really don’t see a markedly higher incidence of tics in my patients with epilepsy, so I really doubt this is a true phenomenon – in other words, the articles fail the real life test,” said Douglas Nordli, Jr. MD, chief of the division of pediatric neurology and co-director of the Neurosciences Institute at Children’s Hospital Los Angeles. However, “focal or multifocal seizures without alteration of consciousness could be mistaken for tics – one example would be myoclonic seizures in which there is a sudden jerk of a body part without any alteration in mentation,” he told Neurology Advisor.

In fact, Dr Sethi and colleagues published a case report in 2007 describing a patient who had been misdiagnosed with a tic disorder when she actually had JME.⁵ “As there is no loss of consciousness with these jerks, these patients may be misdiagnosed as having a movement disorder like a tic disorder and treated inappropriately,” according the report. The 21-year-old college student had been referred after her mother observed the patient having a convulsion. Her regular neurologist ordered a routine EEG and a brain MRI upon her admission to a local hospital, and the results of both tests were normal. The patient was then transferred to Weill Cornell for video-EEG monitoring, with a presumptive diagnosis of complicated tics vs non-epileptic seizures.

A review of the patient’s medical history revealed that she had been healthy until age 16, when she began having sudden jerking of the arms and legs with no impairment of consciousness. The frequency of these movements varied such that she might have 2 on a given day but then experience clusters of them on other days.  At that time, the patient consulted the referring neurologist, who diagnosed her with a tic disorder. In the years following that diagnosis, she received a variety of pharmacological treatments for the “tic disorder,” including lamotrigine and pregabalin. “At one point these ‘movements’ were thought to be of psychogenic origin by her treating physicians,” wrote Dr Sethi and colleagues.

The patient had an uneventful birth, no history of meningoencephalitis, head trauma, or other comorbidities, and no family history of seizures. Examination showed that the cranial nerves and higher mental function were normal, as were the muscle power of all 4 limbs and the deep tendon and plantar reflexes. Video-EEG monitoring was conducted, during which the patient had numerous push-button events. Some of these involved sudden jerks of either arm, while other instances involved the trunk and head. She had multiple myoclonic body jerks that occurred in the early morning and roused her from sleep. “Electrographically they were time locked with generalized polyspikes on the EEG record,” wrote the authors. “A seizure disorder of generalized myoclonic epilepsy was diagnosed and she was started on valproic acid (depakote). At the time of this writing she is ‘seizure’ and ‘tic’ free,” they reported.

This case illuminates a few key differences that often distinguish tics from myoclonic jerks: The leading symptom of JME is jerky movements that typically occur in the morning upon awakening and do not usually recur in the same body part like tics do.⁶ Additionally, tics are commonly preceded by an urge or uncomfortable sensation that is temporarily relieved by the tic, and most people with tics are able to voluntarily suppress them for a brief time if asked, said Dr Sethi; these factors do not apply to myoclonic jerks.

These findings underscore the importance of a thorough history and exam, including the use of video-EEG if necessary. Dr Nordli adds that even home videos can provide valuable information. “Nowadays, inspection of home videos from mobile phones can be extremely helpful,” he said. EEGs should include a sleep section so as not to miss the usual morning pattern of myoclonic seizures, and photic stimulation during the EEG may be another valuable tool, as it will produce typical abnormalities in 25 to 40% of JME patients.⁷ Differentiating tic disorders from myoclonic epilepsy is relatively simple and can prevent unnecessary damage from undiagnosed epilepsy, as well as inappropriate treatment due to misdiagnosis.

References

1. Vaou O, Hohler AD. A case of mistaken identity: juvenile myoclonic epilepsy manifesting as a tic disorder. J Neurol Neurophysiol. 2012; 3:125.
2. Kurlan R, McDermott MP, Deeley C, et al. Prevalence of tics in schoolchildren and association with placement in special education. Neurology. 2001; 57(8):1383-1388.
3. Wong LC, Huang HL, Weng WC, et al. Increased risk of epilepsy in children with Tourette syndrome: A population-based case-control study. Res Dev Disabil. 2016; 51-52:181-7.
4. Weng WC, Huang HL, Wong LC, et al. Increased risks of tic disorders in children with epilepsy: A nation-wide population-based case-control study in Taiwan. Res Dev Disabil. 2016; 51-52:173-80.
5. Sethi NK, Labar D, Torgovnick J. Myoclonic epilepsy masquerading as a tic disorder. Clin Neurol Neurosurg. 2007; 109(6):509-11.
6. Shprecher D, Kurlan R. The management of tics. Mov Disord. 2009; 24(1): 15–24.
7. Epilepsy Foundation. Why is JME so often misdiagnosed? Retrieved on 7/20/16 from https://www.neurologyadvisor.com/home/topics/movement-disorders/tourette-syndrome-tic-disorders-are-highly-heritable/