Glabellar Tap (Myerson’s Sign)

The glabellar tap, also known as Myerson’s sign, is a neurological examination technique used to assess a patient’s response to repetitive tapping on the glabellar region, which is the area between the eyebrows and above the nose. This sign is particularly relevant in the context of Parkinson’s disease and other neurological disorders

Definition of Myerson’s Sign

Myerson’s sign is defined as the persistence of blinking or an involuntary eye blink response upon repeated tapping of the glabellar region. In healthy individuals, the blink reflex typically diminishes after a few taps, while in individuals with certain neurological conditions, such as Parkinson’s disease, the blink response may continue despite repeated stimulation.

Mechanism of Myerson’s Sign

1. Blink Reflex Pathway: The blink reflex is mediated by the trigeminal nerve (cranial nerve V) and the facial nerve (cranial nerve VII). Stimulation of the glabellar region activates sensory receptors, which send signals to the brainstem, leading to the activation of the motor pathways responsible for blinking.
2. Basal Ganglia Dysfunction: In conditions such as Parkinson’s disease, there is often dysfunction in the basal ganglia, which plays a crucial role in regulating motor control and inhibiting reflexive movements. This dysfunction can lead to an exaggerated or persistent blink response when the glabellar region is tapped.
3. Inhibition Failure: The inability to inhibit the blink reflex after repeated stimulation may indicate a disruption in the normal inhibitory mechanisms of the central nervous system, particularly involving the basal ganglia and frontal cortex.

Clinical Significance of Myerson’s Sign

Myerson’s sign has several important clinical implications:

1. Indicator of Parkinson’s Disease: The presence of Myerson’s sign is often associated with Parkinson’s disease and can serve as a clinical marker for the condition. It reflects the underlying basal ganglia dysfunction characteristic of the disease.
2. Assessment of Neurological Function: Myerson’s sign can provide valuable information about the integrity of the neural pathways involved in the blink reflex and the functioning of the basal ganglia.
3. Differential Diagnosis: The presence of Myerson’s sign can help differentiate Parkinson’s disease from other movement disorders and neurological conditions that may present with similar symptoms.

Assessment of Myerson’s Sign

1. Preparation: The patient should be seated comfortably in a well-lit environment. The examiner should ensure that the patient is relaxed and attentive.
2. Tapping the Glabellar Region: The examiner gently taps the glabellar area (the space between the eyebrows) using a finger or a small object. This should be done in a rhythmic manner.
3. Observation of Response: The examiner observes the patient’s response, noting whether there is a persistent blink response after several taps. In healthy individuals, the blink reflex typically diminishes after a few taps, while in individuals with Parkinson’s disease, the blink response may continue.
4. Documentation: The results of the assessment should be documented as either positive (persistent blink response) or negative (normal response).

Differential Diagnosis

1. Parkinson’s Disease: The most common condition associated with Myerson’s sign, characterized by bradykinesia, rigidity, and tremor.
2. Progressive Supranuclear Palsy (PSP): A neurodegenerative disorder that can present with similar symptoms to Parkinson’s disease but may have distinct features, such as vertical gaze palsy.
3. Multiple System Atrophy (MSA): A condition that affects the autonomic nervous system and can present with parkinsonian features, including Myerson’s sign.
4. Dementia with Lewy Bodies: A type of dementia that can present with parkinsonian symptoms and may also exhibit Myerson’s sign.
5. Other Movement Disorders: Conditions such as essential tremor or dystonia may also be considered, although they typically do not present with Myerson’s sign.

References

• Adams, R. D., Victor, M., & Ropper, A. H. (2014). Principles of Neurology (10th ed.). McGraw-Hill.
• Merritt, H. H., & McDonald, J. W. (2010). Neurology (12th ed.). Lippincott Williams & Wilkins.
• Kandel, E. R., Schwartz, J. H., & Jessell, T. M. (2013). Principles of Neural Science. McGraw-Hill.
• Jankovic, J. (2008). Parkinson’s Disease: Clinical Features and Diagnosis. Journal of Neurology, 255(Suppl 5), 1-6.