Babinski, Pseudo-Babinski, and Dystonia—Reply

In reply

We thank Dr Horstink and colleagues for their interest in our article¹ and for their informative comments regarding the neurophysiological basis of the extensor plantar response in patients with pyramidal tract dysfunction and the putative neurophysiological mechanisms responsible for the “pseudo-Babinski” response in patients with dystonia. The focus of our manuscript was to broaden the phenotype of DRD and to highlight the fact that patients with genetically confirmed DRD may have “cerebellar signs” that may also improve in response to levodopa therapy. Nevertheless, some points raised by Horstink et al deserve discussion.

There have been several reports of patients with DRD presenting with clinical features suggestive of spasticity,^{2 - 4} resulting in the initial misdiagnosis of hereditary spastic paraparesis or cerebral palsy^{5 - 6} and a subsequent inadvertent delay in the commencement of levodopa therapy. We accept that hyperreflexia and apparently extensor plantar responses may be seen in patients with extrapyramidal dysfunction or dystonia and agree that the alteration of these clinical findings in our affected family members in response to levodopa may lead one to speculate that these findings were originally “extrapyramidal” or “dystonic” rather than “pyramidal” in origin. Some family members may have had striatal or dystonic toes, but one cannot completely exclude reversible upper motor neuron dysfunction in others. One does not expect to find limb spasticity in a patient with pure dystonia or extrapyramidal dysfunction as observed in the nondystonic limbs in patient 1 in our family.¹ At present, there are too few neuropathological studies to definitely exclude pathological evidence of pyramidal tract involvement in DRD, but current and future functional imaging data should shed further light on the function (or dysfunction) of the upper motor neuron tracts or their connections in DRD.⁷

The authors refer to previous studies on the interpretation of abdominal reflexes. Although medical students are often taught that the absence of abdominal reflexes suggests an upper motor neuron lesion, we find this sign notoriously unreliable. Patients may have absent abdominal reflexes in a variety of settings that do not indicate upper motor neuron dysfunction, eg, following childbirth (especially in multiparous women), following abdominal surgery, in overweight patients, and in patients with lower motor neuron disease, such as acute inflammatory demyelinating polyradiculoneuropathy, affecting the lower thoracic spinal roots.

Horstink and colleagues suggested certain clinical features that may help differentiate between a true Babinski response secondary to pyramidal tract dysfunction and a pseudo-Babinski response secondary to Parkinson disease. Although spontaneous dorsiflexion of the hallux major on standing or walking may occur in patients with extrapyramidal disease, this is not a specific sign of extrapyramidal disease and may also occur in some patients with definite upper motor neuron dysfunction, eg, multiple sclerosis. We must also emphasize that the extensor plantar response may last for several seconds and not just for “a few hundred milliseconds” after removal of the stimulus from the sole of the foot in patients with severe lower limb spasticity. We feel it more important to interpret the plantar responses in the context of the rest of the detailed neurological examination rather than in isolation. It was not the focus of our family study to do simultaneous electromyography of the lower limb flexors and extensors while assessing the plantar responses. However, we agree that further detailed neurophysiological studies may improve our understanding of the pathophysiological basis for extensor plantar responses in patients with pyramidal tract and dystonic disorders.

Correspondence: Dr Murphy, Department of Neurology, Adelaide and Meath Hospital (incorporating the National Children's Hospital), Tallaght, Dublin 24, Ireland (raymond.murphy@amnch.ie).

Financial Disclosure: None reported.