Areflexia

AREFLEXIA, the absence of reflexes, usually indicates an existing interruption in the reflex arc, but sometimes reflexes may also be absent as a result of inhibition originating from some part of the central nervous system or from the periphery. The most typical cases of areflexia occur in neuritis, polyneuritis, plexitis, radiculitis, tabes dorsalis, and poliomyelitis. In these cases, areflexia occurs as a result of damage to either the sensory (afferent) neuron (sensory nerve, intervertebral ganglion, posterior root), the motor peripheral neuron (anterior horn cells, anterior root, motor nerve), or the sensory and motor fibers (neuritis). Pupillary areflexia to light is a characteristic symptom of tabes dorsalis (Argyll Robertson sign), progressive paralysis, and syphilis of the nervous system; it is also observed during an epileptic seizure, in hypertrophic interstitial polyneuritis, Charcot-Marie tooth muscular atrophy, and carbon disulfide poisoning; pupillary areflexia also occurs as a result of a previous typhus fever, encephalitis, alcoholism, and in old age. Pupillary areflexia can also be a sign of brainstem damage (cerebral peduncle). Corneal and conjunctival areflexia is noted as a symptom in lesions (tumors) in the posterior cranial fossa. Tendon areflexia—the loss of the knee reflex and others—is observed in intoxication with chloroform, ether, phenol, in diabetes, acute asphyxia, exhaustion (running, competitions), alcoholism, and in old age. The congenital absence of tendon reflexes is regarded as a degenerative sign, most frequently encountered in congenital syphilis. The etiology of monosymptomatic areflexia is unclear; one may assume an infection suffered in childhood. The absence of the knee reflex makes one think primarily of tabes dorsalis, but it is observed not only in this condition; in any case, if areflexia is present, its origin must be determined. The absence of the Achilles reflex in sciatica indicates a deeper character of the underlying process. The absence of abdominal reflexes can be an early symptom of multiple sclerosis. Areflexia is sometimes observed with increased cerebrospinal fluid pressure (brain tumor, brain abscess) and disappears after a lumbar puncture. Areflexia may depend on a disease of the frontal lobes of the brain and spread to isolated reflexes of one side or the other. In acute hemiplegia, a decrease or absence of cutaneous reflexes is usually observed on the paralyzed side. In cerebellar diseases, reflexes are sometimes diminished or even absent. Concussion, cerebral stroke, and spinal cord rupture are usually accompanied by areflexia in the first few days. Sometimes it is possible to elicit previously absent tendon reflexes in a bath, which is explained by the fact that certain subjects, during routine reflex testing, do not know how to relax their muscles.

V. Khoroshko.