Clonus Associated with Tropical Spastic Paraparesis.

A 53-year-old woman with tropical spastic paraparesis (also called human T-lymphotropic virus–associated myelopathy) reported several months of worsening weakness of the legs and feet, which had led to her use of a wheelchair. On examination, she was found to have severe spasticity and weakness of both legs and feet, bilateral Babinski sign, and bilateral patellar clonus (see video). The results of a neurologic examination were otherwise normal. Paraparesis in tropical spastic paraparesis is progressive, and the patient’s condition has followed the anticipated clinical course, with spasticity that has increased over the course of a year and has not responded to treatment with baclofen. Rhythmic muscular contractions after a tendon’s stretch reflex is termed clonus and is most commonly seen at the Achilles’ tendon, but it may also occur during reflex examination of the patella, biceps tendon, and triceps tendon. The underlying cause is excessive excitability of the motor neurons, which produces the contract– relax rhythmic movements that are characteristic of clonus. Clonus is usually a pathologic finding, but a few beats, particularly at the ankles, can be found in healthy persons who have constitutional hyperreflexia.