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Diabetic 3rd nerve palsy: evidence for a mesencephalic lesion
Neurology
|July 1, 1990
Summary
Diabetic patients with isolated third nerve palsy often show abnormal masseter reflexes, suggesting a central cause like a mesencephalic infarct rather than a peripheral nerve issue.
Area of Science:
- Neurology
- Neuroscience
- Ophthalmology
Background:
- Diabetic neuropathy commonly affects cranial nerves, including the oculomotor nerve (3rd nerve).
- Isolated third nerve palsy in diabetics typically presents with ptosis, diplopia, and ophthalmoplegia, sometimes with pupillary involvement.
- The etiology of diabetic third nerve palsy is debated, with peripheral nerve ischemia being the traditional hypothesis.
Purpose of the Study:
- To investigate the underlying pathophysiology of isolated third nerve palsy in adult chronic diabetic patients.
- To explore the diagnostic utility of masseter reflexes (MassR) in differentiating central versus peripheral causes of third nerve palsy.
- To correlate clinical findings with neuroimaging in diabetic patients with third nerve palsy.
Main Methods:
- Retrospective analysis of 11 consecutive adult diabetic patients with isolated third nerve palsy.
- Clinical assessment including pupillary function and masseter reflex testing.
- Magnetic resonance imaging (MRI) to evaluate for brainstem lesions, particularly in the oculomotor fasciculus.
Main Results:
- Ten of eleven patients with isolated third nerve palsy had abnormal ipsilateral or bilateral masseter reflexes.
- Eight patients presented with pupillary sparing.
- Three patients showed MRI lesions in the ipsilateral oculomotor fasciculus; three developed mild brainstem signs.
- Thirteen patients with Weber's syndrome (midbrain infarct) also exhibited abnormal masseter reflexes.
- Seven patients with extra-axial third nerve palsies had normal masseter reflexes.
Conclusions:
- Isolated diabetic third nerve palsy, even with pupillary sparing, is frequently associated with abnormal masseter reflexes.
- These findings strongly suggest a central etiology, specifically a focal mesencephalic infarct, rather than a peripheral nerve lesion.
- Masseter reflex abnormalities may serve as a valuable clinical sign in localizing the lesion in diabetic third nerve palsy.