Sensory perception in leprosy-neurophysiological correlates1

International Journal of Leprosy and Other Mycobacterial Diseases, Jun 2003 by Malaviya, Govind N

ABSTRACT

The loss of sensation in skin lesions, and in a palm or sole that has been innervated by peripheral nerve trunks, is characteristic of leprosy. Detection of early nerve trunk involvement depends on demonstrating sensory loss. Newer developments in neurological sciences have made fresh interpretations of the observed sensory abnormalities in leprosy-affected persons possible. Some of these observations are described in this review, and their implications discussed.

RESUME

Les pertes de sensibilite des lesions cutanees, ainsi que de la plante et la paume qui sont innervees par des troncs de nerfs peripheriques, sont caracteristiques de la lepre. La detections precoce de l'atteinte de troncs nerveux depend de la demonstration de la perte de sensibilite de la paume et de la plante des pieds. De recents developpements en neurologie ont permis de realiser de nouvelles interpretations d'anomalies sensitives observees chez des personnes atteintes de lepre. Certaines de ces observations sont decrites dans cet article et leurs consequences, discutees.

RESUMEN

La perdida de sensacion en las lesiones de la piel y en la palma de la mano o en la planta del pie que han sido inervadas por troncos de nervios perifericos, es caracteristica de la lepra. La deteccion de la afeccion temprana de los troncos nerviosos depende de la demostracion de la perdida sensorial en la palma de la mano o en la planta del pie. Los nuevos desarrollos en las ciencias neurologicas han permitido hacer nuevas interpretaciones de las anormalidades sensoriales en las personas con lepra. Algunas de estas observaciones se describen en este articulo y se discuten sus implicaciones.

Our five senses enable us to experience the world around us. They work in harmony, each contributing in varying degrees. Sensations are so well integrated that the contributions of any one becomes apparent only when that sense is not functioning. Absence of any one sensation may not be detrimental because those remaining usually try to compensate for the deficiency. The process of integrating data through senses seems to be rapid, almost subconscious to the observer, and likely to precede examination of details.

The hand is an important sensory organ. The nerve supply to the palm of the hand is relatively constant, though wider variations are described. The skin of the hand, particularly the palmar surface, is richly innervated and supplied with all types of skin sensory receptors. Receptors for touch, though present all-over the body, are concentrated in the palm of the hand. Fingernails can also judge textures and shapes in cases where skin sensations are absent (3). Based on information continuously provided by the hand and all its appendages, one can decide whether an object is of interest and safe or is uninteresting and dangerous. It is not until we are without the ability to experience tactile stimuli-hot or cold, pain or pressure, position or proprioception-that we realize the importance of touch in our lives.

Sense of touch is probably not given that much importance by those who have all their sensory functions intact, especially those with unimpaired vision. However, a blind person, who depends upon his hands to explore and appreciate his environment, has a different perception of surroundings compared to his sighted colleagues. He understands how much the role of the hand as a sensory organ has been neglected (1).

Very few people realize the precision of perception of the fingertips and palm, and underestimate the acuity with which finer details can be appreciated through them. A sensate hand can give an instant picture of the overall shape, size, weight, and general texture of an object. Still finer details can be appreciated by feeling the vibrations produced by running the free ends of the fingernails across the surface or edge of an object (3).

These extraordinary sensory capacities of the human hands have a long evolutionary history. The hand, as a complex unit of muscles, tendons, and bones could not function properly, with its versatility, flexibility and power, without the ability to feel. Touch is far more than a means of observation; it is also a source of esthetic and sexual pleasure. Much beauty in objects can be appreciated by anyone through the sense of touch. Touch may reveal that some surfaces are genuinely ugly to the touch even if they appeal to eye, e.g., a beautifully carved nose with a rigid implant.

PHYSIOLOGY OF SENSORY PERCEPTION

Sensory modalities. Von Frey established the doctrine of four energies in the form of pressure, warmth, cold, and pain. The other senses are believed to be perceptual interactions of pressure and pain sensations. There are four primary modes of sensations: touch, pain, cold, and warmth. Pressure sensation may be derived from the activity of both cutaneous and deep sensory mechanisms, and therefore it is more of a concept than a primary sensation. The relation of pin-prick pain to light pressure is obscure. Normal skin does not respond to temperature variations within or -5[degrees]C of the existing skin temperature.