| The clonic response or reflex with clonus is an extreme exaggeration of a physiological response. When scales of graduation are employed —although imprecise, they are popular—it would be treated as a grade 4 hyperreflexia.
The Achilles reflex is elicited with the patient in supine position, thigh flexed above the hip and heel flexed towards the thigh. The foot is placed in light hyperextension and is struck with a tendon hammer on the Achilles tendon. The physiological response consists of plantar flexion of the foot. Occasionally the response consists of repetitive jerks in flexion facilitated by maintaining a light forced hyperextension.
In the video an alternative way of eliciting the reflex is shown. Instead of striking the tendon, we abruptly hyperextend the foot on the leg, maintaining slight hyperextension at the end of the movement. As can be seen the response consists of repeated jerks in flexion. Occasionally the jerks peter out after 6 or 7 repetitions, but on other occasions they are maintained while hyperextension of the foot is maintained.
It is significant because it is suggestive of a pyramidal tract lesion, usually contralateral cerebral lesions (upper motor neuron lesion). Therefore it is a sign that will be found in the context of spasticity of the extremities, with greater or lesser degrees of paralysis and hyperreflexia, without alterations in sensation. The clonus response can be obtained in other joints, for example, the knee.
The case presented here was as a consequence of Listeria monocytogenes meningitis that caused a tetra-ventricular hydrocephalus and serious and extensive lesions in the brain. In this case the affected areas of the motor cortex and/or the pyramidal tracts and their nuclei are responsible. In Fig 1 and 2 extensive lesions of the cortex and subcortical areas can be seen and can be compared with similar cuts of a normal CT (Fig 3).
More information and test questions on listeriosis can be found in the "image of the month" of December 2007.
Autor:
Juan Ignacio
Pérez Calvo
Servicio de Medicina Interna
Hospital Clínico Universitario
Zaragoza
Translation: Kelly
Watt
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