Chapter 13 Differential Diagnosis of Acquired Causes of Spastic Paraplegia

Publisher Summary This chapter describes the common neurologic disorders causing spastic paraplegia and the most efficient way to arrive at an etiologic diagnosis. Spastic paraplegia is caused by lesions affecting the upper motor neuron or axons originating from it in the corticospinal, also termed “pyramidal,” tract. Spastic paraplegia is characterized by an abnormal gait, which is, in most cases, recognizable at first glance. The legs are stiff, extended at the knees and at the ankles, with a tendency for an adduction, causing the “scissor gait.” The gait paradoxically may be fast in some cases or slow and labored depending not only on the degree of spasticity but also on the degree of the concomitant weakness. Clinical examination shows stiffness in the legs reinforced by movements, pyramidal reflexes, and a bilateral Babinski sign. It is not unusual to note dissociation between the severity of symptoms and signs. This discrepancy is important to know because it may lead to a false appreciation of the level of disability of the patient. For example, in hereditary spastic paraplegia or cerebral diplegia, spasticity may severely invalidate the gait, although particular movements are easily performed and only minor changes in the reflexes are observed. Sometimes, pyramidal signs such as spasticity, weakness, and abnormal reflexes may become evident only after exercising. It is therefore useful when the neurologic examination findings are normal at rest to perform it after exercising.