Symptoms of sensory disorders

Main symptoms: deficit and irritation

All somatic sensory disorders are divided into two broad categories: negative (when perception decreases or disappears) and positive (when excessive or distorted sensations arise).

Negative symptoms ("deficit symptoms") include:

• Anesthesia and hypesthesia — complete loss or partial reduction of various types of sensitivity (tactile, thermal, vibrational).
• Analgesia and hypalgesia — loss or blunting exclusively of pain perception.
• Astereognosis — inability to recognize an object by palpation, despite the patient's preserved basic sensory modalities.

Positive symptoms ("irritation symptoms") are more diverse and often cause severe discomfort to the patient:

• Paresthesia — a sensation of "pins and needles", tingling, or tightness that occurs spontaneously or upon light touch.
• Hyperesthesia and hyperalgesia — inadequately strong perception of normal stimuli or weak painful stimuli.
• Allodynia — a condition in which a touch that is normally not painful is perceived as painful.
• Hyperpathia — a distorted, extremely unpleasant sensation with an aftereffect component (persists after the stimulus is removed). The sensory threshold may be paradoxically elevated.
• Neuralgia — sharp, piercing pains resembling an electric shock. They last for seconds and spread strictly along the innervation zone of a specific nerve.
• Causalgia — a burning, unbearable pain that is invariably accompanied by local autonomic (vegetative) dysfunctions: changes in skin color and temperature.

Pathogenetic classification of pain

Pain is the most frequent and significant positive symptom. According to the mechanism of development, it is divided into three types:

1. Nociceptive pain. Occurs with actual tissue damage (skin, bones, internal organs) and the activation of pain receptors. It can be felt at the site of injury or projected to distant areas (referred pain). A classic example is pain radiation to the left arm and jaw during acute myocardial ischemia.
2. Neuropathic pain. Associated with damage to the structures of the nervous system itself responsible for conducting or inhibiting pain. Receptors may be intact, but ectopic impulse generation occurs in nerve fibers. Examples: phantom pain in an amputated limb, trigeminal neuralgia. Antidepressants and antiepileptic drugs are used for treatment.
3. Psychogenic pain. Diagnosed when there is no organic cause, or the intensity of complaints clearly does not correspond to the severity of the lesion. It often occurs against the background of depression or anxiety disorders.

Acute and chronic pain

By duration, pain syndrome can be transient, acute, and chronic.

• Acute pain is a normal protective reaction of the body to injury (mechanical, thermal). It is treated by eliminating the cause and prescribing analgesics.
• Chronic pain lasts for more than three months or persists after tissues have healed. It is always accompanied by dysfunction of the antinociceptive system — the structures of the spinal cord, reticular formation, and thalamus, which normally inhibit pain signals. Chronic pain therapy aims to suppress the conduction of pain impulses and stimulate the body's own inhibitory systems.

Methods for examining sensitivity

Objective examination is always based on comparative analysis: the physician compares sensations in symmetrical areas of the body, as well as in proximal and distal zones. When abnormalities are detected, their boundaries must be precisely outlined.

How individual sensory modalities are examined:

• Tactile: using a cotton ball or calibrated synthetic filaments (Frey's hairs).
• Temperature: test tubes with warm (+40–50 °C) and cold (+15–25 °C) water or a special instrument—the thermopen—are used.
• Vibratory: the base of a vibrating tuning fork (128 or 256 Hz) is placed on bony prominences (joints, ribs, spinous processes).
• Joint-position (proprioception): the physician performs passive movements in the patient's joints (starting from the terminal phalanges of the fingers). Normally, a person with closed eyes feels a minimal position change of 1–2°.
• Two-dimensional spatial (graphesthesia): numbers or simple shapes (crosses, circles) are drawn on the patient's skin with a blunt object, which they must recognize.

Class and exam questions

What else to study on this topic

• Innervation scheme of head dermatomes by the trigeminal nerve (Nervus trigeminus).
• Strip-like distribution of sensitivity on the upper extremities (Cervicalia and Thoracica segments).
• Innervation of the gluteal region and perineum by lumbar and sacral segments (Lumbalia, Sacralia).
• Mechanism of action of antiepileptic drugs in neuropathic pain (blockade of ectopic impulses).
• Influence of psychological factors on the modulation of pain syndrome.

Other topics in «Chapter 1. Disorders of Somatic Sensation»

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.