A Weak Jaw Says Much
Abstract & Commentary
By Michael Rubin, MD, Professor of Clinical Neurology, Weill Cornell Medical College. Dr. Rubin reports no financial relationships relevant to this field of study.
Synopsis: Careful testing of jaw muscle power can help to make an accurate clinical diagnosis in acute, flaccid quadriparesis.
Source: Pal S, Sanyal D. Jaw muscle weakness: A differential indicator of neuromuscular weakness preliminary observations. Muscle Nerve 2011;43:807-811.
Guillain–barré syndrome (GBS), inflammatory myopathy including polymyositis and dermatomyositis (PM/DM), myasthenia gravis (MG), and hypokalemic periodic paralysis (HPP) are among the more common causes of flaccid quadriparesis confronting neurologists in the emergency department. Although often differentiated by characteristic clinical or electrodiagnostic features, this is not always the case, and acute flaccid quadriparesis may present a clinical conundrum to the physician on the neurology ward or emergency department. Do any clinical features permit one to reliably discriminate between these diagnostic possibilities at the bedside?
Between January 2008 and December 2009, patients admitted with acute quadriparesis to the Bangur Institute of Neurosciences, West Bengal, India, were recruited into this prospective, double-blinded study. Exclusion criteria included signs of upper motor neuron involvement or altered sensorium of any cause. Clinical evaluation included thorough neurologic examination with particular attention to strength testing of jaw and neck muscles, blood tests (including acetylcholine [ACh] receptor antibody assay), electrodiagnostic studies (including repetitive nerve stimulation), and muscle biopsy when clinically indicated. Definitive diagnosis was based on repetitive nerve stimulation studies and ACh receptor antibody assay for MG, histopathology for PM/DM, serum potassium level for HPP, and nerve conduction studies for GBS. Statistical analysis included the chi-square test, Fisher exact test, or Monte Carlo approximation, with P < 0.05 considered statistically significant.
Among 46 patients who fulfilled the inclusion criteria, GBS was the final diagnosis in 24, generalized MG in 9, HPP in 6, PM in 4, and DM in 3. Weakness of jaw closure was the most clinically reliable diagnostic sign, with all such patients having MG. Among MG patients, 88% (8 of 9) had jaw closure weakness. In the absence of jaw closure weakness, weakness of jaw opening became the most significant diagnostic predictor, found in 83.3% (5 of 6) of HPP, and 71.4% (5 of 7) of inflammatory myositis, but only 4.1% (1 of 24) of GBS patients. Among patients with normal jaw strength, 85.2% had GBS, which increased to 100% if areflexia of the legs was present. Weakness of jaw opening but not closing, in the absence of pharyngeal weakness, was diagnostic of HPP. If both jaw opening and pharyngeal weakness were present, PM/DM was the final diagnosis. Jaw muscle weakness is rare in GBS, jaw closing weakness favors MG, and jaw opening weakness PM/DM or HPP.
Local disorders that affect the trigeminal nerve often result in facial numbness, dysesthesiaes, or paresthesiaes, rather than jaw muscle weakness, and include intra-axial lesions, such as stroke, tumor, demyelinating disease, infections and inflammatory conditions (including collagen vascular diseases such as Sjogren's syndrome, systemic lupus erythematosus, and scleroderma) and extra-axial lesions (including aberrant blood vessels, aneurysms, meningiomas, carcinomatous meningitis, and spread of extracranial primary malignancies). Magnetic resonance imaging usually is warranted in all such instances, and electrodiagnostic tests that may be of benefit include the blink reflex, the masseter inhibitory reflex, the jaw jerk reflex, nerve conduction study of the mental nerve, and quantitative sensory testing of patients with sensory symptoms.