Abstract
Rapidly developing flexion contractures of the lower extremities in multiple sclerosis (MS) is a devastating neurological complication that markedly affects quality of life and cost of care. The swiftness of conversion from uncontrolled extensor posture of the legs to fixed flexion, which occurred within weeks in these two patients with longstanding extensor rigidity, has not been previously emphasized. Spinal cord flexor reflex afferents are subject to tonic inhibition from the brainstem by the dorsal reticulospinal pathway. Extensor tonic reflexes in the lower extremities are facilitated by the vestibulospinal tract, as well as part of the reticulospinal tract arising dorsolaterally in the medulla. Spinal cord lesions that interrupt these descending tracts result in tonic flexion of the lower extremities. The demonstration of spread in the size of the receptive field and of the type of stimuli that can elicit flexor responses in spinal cord lesions has therapeutic implications. Neurological rehabilitation must anticipate the sudden development of flexor spasms leading to fixed flexion posture in all MS patients. The presence of a triple flexion withdrawal response to plantar stimulation that breaks through the extensor rigidity is a warning sign of impending fixed flexion. In addition to this vigilance, the physician must aggressively treat these patients. Diligent attention to skin and bladder care will reduce the stimuli to the large receptive zone for flexor spasms. Early physical therapy, antispasmodic medications, and, when needed, orthotic devices must be prescribed to maintain the patient's ability to sit.