Unilateral shivering: a result of lateral medullary infarction.

Abstract: Shivering is mediated via the predominantly uncrossed reticulospinal tract. We report a case of a patient with left lateral medullary tract infarct involving the reticulospinal tract who displayed ipsilateral absence of shivering during a febrile episode. The physiology and anatomy of shivering and the reticulospinal tract is reviewed.

Key Words: unilateral shivering, reticulospinal tract, lateral medullary infarct

**********

Shivering is mediated via the predominantly uncrossed reticulospinal tract. The present case report may be the first to relate a unilateral neurologic problem to disease of the reticulospinal tract. Accordingly, a brief review of our current understanding of the physiology and anatomy of shivering and the reticulospinal tract is included.

Case Report

In 2005, a 75-year-old diabetic retired orthopedist experienced the onset of irregular, painless jerking and shaking of his right upper extremity and to a much lesser extent, his right lower extremity, without impairment of consciousness. This continued for three hours, with mild spread to his left shoulder, while his temperature rose to 100.2 degrees. He had also noted an increased frequency of urination, and when urinalysis revealed pyuria, he was given a single dose of 650 mg of aspirin, after which the shaking promptly ceased.

He had ten years earlier experienced a stroke characterized by ataxia and the loss of thermal sensation in the right arm. The neurologic examination then found a left-beating clockwise rotary nystagmus on the left lateral gaze and a horizontal and milder right-beating nystagmus on the right lateral gaze. The left corneal reflex was hypoactive and left trigeminal thermal and pinprick sensation were diminished, particularly in the ophthalmic and maxillary distributions, but there was no weakness of the face or extremities. Vibratory sensation was absent in the distal lower extremities, and there was short-stocking hypalgesia. The right lower extremity was dysesthetic to pinprick. A left lateral medullary infarct and diabetic neuropathy were diagnosed. The MRI of the brain was normal, while the brainstem auditory-evoked response (BAER) and the blink reflex study were both consistent with left lower pontine infarction. A recent MRI (Fig.) showed an old left lateral medullary, rounded infarct corresponding to the location of the trigeminal spinothalamic nucleus and tract.

Discussion

This retired orthopedist reported the onset of an irregular jerking of his right arm (predominantly the shoulder) and to a lesser degree, his right leg, that had already persisted for several hours. Epilepsia partialis continua was suspected, but the concurrent development of urinary frequency and low-grade fever raised the possibility of a shaking chill that was suppressed on his left side by his old left lateral medullary infarct. This diagnosis was well supported by his remaining mentally intact, even after three hours of right-sided shaking, the absence of rhythmicity, concurrent fever and pyuria, prompt response to aspirin without use of any antiseizure medication, and the absence of cerebral lesion on MRI scan, which confirmed that his stroke ten years previously had been a small lateral medullary infract. No further attacks have occurred over the ensuing ten months.

[FIGURE OMITTED]

The neuroanatomical basis of shivering is well understood. Thermosensitive neurons within the preoptic hypothalamus are of two types: warm-sensitive neurons whose firing increases as preoptic temperature rises, and cold-sensitive neurons whose firing increases as preoptic temperature falls and whose action induces shivering. (1-3) The efferent pathway of these cold-sensitive preoptic neurons traverses the median forebrain bundle to terminate in the posterior hypothalamus, where axons proceed caudally through the mid-brain dorsolateral to the red nucleus to reach reticulospinal neurons located within the reticular formation of both the pons and medulla. These reticulospinal neurons give rise to the reticulospinal tract which occupies a lateral position within the pons, medulla, and spinal cord, and is predominantly ipsilateral; (2) at every level, lesions along the reticulospinal tract abolish shivering, while no effect upon shivering has been produced by extensive medial lesions or by lesions of the pyramidal tract and periventricular areas. (3) Most reticulospinal tract fibers synapse on interneurons in lamina VII and VIII (1,3) of the ventral horn, most abundantly within the cervical spinal cord, (2) and function in the control of movements not requiring conscious effort (such as the maintenance of posture and shivering). Reticulospinal impulses alter muscle spindle sensitivity, thus modulating myotatic reflex sensitivity, but the rhythm for shivering probably reflects the generation within a spinal cord neural network of a rhythmical neural signal whose amplitude is controlled by the intensity of tonic reticulospinal signal. (4)

This patient had previously experienced an ischemic lateral medullary syndrome involving the left trigeminal spinothalamic nucleus and tract and probably also the left reticulospinal tract, with the result that he could no longer shiver on the left side of his body. Both the patient and his wife emphasized the "jerking" of his right upper extremity, particularly about the shoulder, and his wife noted similar movements of the right lower extremity. A single dose of aspirin alleviated the shaking, and studies subsequently revealed pyuria caused by Pseudomonas aeruginosa urinary tract infection sensitive to ciprofloxacin and clinically responsive to that antibiotic; there has been no recurrence subsequent to this effective treatment. Literature review has found no similar instances of unilateral shivering caused by neurologic disease.

References

1. Boulant JA. Role of the preoptic-anterior hypothalamus in thermoregulation and fever. Clin Infect Dis 2000;31:S157-S161.

2. Kiernian JA. The Human Nervous System: An Anatomical Point of View, 8th ed. Philadelphia, Lippincott, Williams and Wilkins, 2005.

3. Boulant JA. Hypothalamic control of thermoregulation: neurophysiologic basis. In: Morgane PJ, Panksepp J (eds). Handbook of the Hypothalamus, Vol 3, Part A. New York, Marcel Dekker, 1980, pp 1-82.

4. Horwitz BA. Homeostatic responses to acute cold exposure: thermogenic responses in birds and mammals. In: Handbook of Physiology. Section 4: Environmental Physiology Vol I. New York, Oxford University Press, 1996, pp 359-377.

Gordon J. Gilbert, MD

From the Department of Molecular Pharmacology and Physiology, University of South Florida School of Medicine, Tampa, FL.

Reprint requests to Dr. Gordon J. Gilbert, 500 Pasadena Avenue South, St. Petersburg, FL 33707. Email: [e-mail]

Accepted October 16, 2006.

RELATED ARTICLE: Key Points

* Shivering is mediated by the predominantly uncrossed reticulospinal tract.

* A patient with left lateral medullary infarct involving the reticulospinal tract displayed ipsilateral absence of shivering when he became febrile from a urinary tract infection.

* The present case is thought to be the first to relate a unilateral injury of the reticulospinal tract in a human to a clinical manifestation: the ipsilateral absence of shivering.