Sensory and its disorders. Pain. Syringomyelia

Sensory is the ability to experience at least external and internal stimuli. It can be divided into general sensory (pain, temperature, tactile, etc.) and special sensory (vision, hearing, smell, taste). This topic consider only general sensory.

Brief anatomy and physiology of the general sensory

It depends on localization of receptors, it’s divided into superficial sensory (pain, temperature, tie-straightening), or exteroreceptor and deep sensory (joint-muscular sensory, vibration sensory), or proprioreceptor (receptors located in muscles, tendons, ligaments, capsules of joints) and interoreceptor (baro-, chemoreceptor located in the internal organs) as a complex species sensory allocate stereognosis (stereognosis sense), two-dimensional sense.

Picture 1 shows the path of pain and temperature sensory.

First neuron, which receives irritation from pain or thermal receptor, situated in the spinal cord ganglia. Excitation from the receptor spreads along its dendrites, in coming in the part of peripheral nerve and plexus and, reaches the body neuron and distributed by its axon, which go thru posterior root and reaches the posterior horn, where placed second neuron. More excitation spread along the axon of the second neuron, which passes on opposite side thru anterior commissure and enter in the lateral funiculus, giving a branch for the formation of segmental reflex pathway. Goes to the opposite side occurs in the oblique plane, therefore axon enters to lateral funiculus in 1 -2 segments level higher than second neuron. Axon of the second neuron passes through the spinal cord, brain stem and reaches thalamus, forming TRACTUS SPINOTHALAMICUS. At the level of the spinal cord in spinothalamic pathway marked eccentric location axons, in which fibers carry information from the lower limbs, located laterally, fiber from upper limb - medially (fibers from the trunk located between them). In thalamus excitation is transmitted to a third neuron, axon which forms TRACTUS THALAMOCORTICALIS, passes thru posterior arm of internal capsule, white matter of cerebral hemisphere and reaches post central gyrus of the parietal lobe. In the upper part of the post central gyrus and the medial part (paracentral lobe), parietal lobe receives information about the lower extremities, in the middle part - about trunk, upper extremity, and the lower part - about the face and internal organs.

The first neuron is the pathway of deep and tactile sensory (see Fig. 1), which receives stimuli from definite receptor (tactile corpuscles of the skin, receptors of muscles, ligaments, tendons, joint capsules), reaches in spinal ganglia. Initiation from receptor is distributed according to its dendrite, incoming in the peripheral nerves and nerve plexus and reaches the body of the neuron and extends on its axon, which is in the

posterior root enters posterior cord of its side, giving at this level branch for the formation of the segmental reflex. Axons of neurons from the lower limb form a thin bundle (bundle Gaulle/Голля), which is located medially; axon of neurons from the upper limbs form klinovidniy bundle (Burdach's nucleus/Бурдаха),

which is located laterally in the posterior horn. Axons of neurons in the second part of the new bundle (laminiscus medialis) go to the opposite side and join the fibers of pain and temperature-sensitive, reaching with the thalamus. In the thalamus the excitation is transferred to the third neuron, whose axon, forming TRACTUS THALAMOCORTICALIS which passes through the posterior horn of internal capsule, white matter of brain and reaches post central gyrus of parietal lobe. In the upper part of post central gyrus and media part (paracentral lobe) of the parietal lobe, receives information from the lower extremities, in the middle part - the trunk and upper extremity, the lower part - of the face, the internal organs.

Thus, the different localization of conductors pain, thermo sensory and deep, tactile sensory are observed in the spinal cord and medulla of brain, in other parts of the nervous system of conductors of various types of general sensory are placed together.

Methods of Diagnosis of General Sensory

Studies are started from clarifying the complaints (pain, numbness, the unpleasant sensations) and, if they exist, must specify their nature and localization. Then put different kinds of stimulation, determining the existence of sensations (pain, heat, etc.) and comparing the sensations in symmetrical of body parts, distal and proximal parts of extremities. At identifying changes must determine their localization and borders, compare external region with the limits of anatomical innervations. Pain sensory is determined with the injection of needle, which should be strong and frequent. For study of temperature sensory, must use test tube with cold (+15 ...+ 25 ° C) and hot (+40 ... +50 ° C) water or with cooler or warmer (in comparison with patient’s skin) objects, such as metal part of neurological hammer. For assessment of deep sensory mostly always study joint-muscular sensory - a feeling passive movements in the joints of limbs. Survey shows, types of movements that will be produced, for example upwards or downwards, then asked to close their eyes and determine patient doctor passive movement. Usually, studies begin with the definition of passive movements in the terminal phalanx of limbs, and then move to the larger big joints. Healthy people feel light passive movement in the joint (change position at 1-2 °). With the help of a tuning fork can be investigated - vibration sensation; leg vibrating tuning fork will set on the bone protrusion and define whether patient feels the vibration or not, If yes must measure the duration of vibration felt, which is normal 9 – 15 seconds.Tactile sensory studies is done by light touch to soft skin of palm or sole ; patient is asked to close their eyes and whether he feels the touch, say" yes ".

In complex forms of sensory usually investigate two dimensional senses and stereognosis. To estimate two dimensional senses on patient’s skin must use blunt objects, such as blunt end of the needle, drawing some shapes (circle, cross, triangle), which he must identify with the eyes closed. To assess Stereognosis must asked patient to close eyes, put his arm on known object (key, coin, pencil, etc.) and ask him what the object is. A healthy person does flawlessly.

Symptoms of sensory disorders

Sensory disorders can occur with lesions of conductors general sensory to different levels: brain, cranial nerves, spinal cord, posterior root, plexus, and peripheral nerves. They are show in the form of symptoms of irritation, such as pain and loss - loss of sensitivity). As the basis symptoms of sensory disorders are distinguished pain, paresthesia, hypoesthesia, anesthesia, hyperesthesia, dysesthesia and hyperpathia. Paresthesia – discomfort feeling in the form of pricking, numbness and crawl of small insects/ chills. Hyperesthesia - increased perception of touch, or any other skin irritation. Hypoesthesia – desensitization/decrease sensation, anesthesia - about the total loss. The reduction in pain

sensitivity is like hypalgesia, its total loss - analgesia. When there is lesion in all conductors overall sensitivity (in example, when trauma of nerves) develops a total anesthesia, when isolated lesions – loss of one type of sensory (dissociated type of sensory disorder). Loss of deep sensitivity (joint – muscle sensory) is accompanied by muscle hypotonia and hyporeflexia, it leads to movement disorders - sensory ataxia. Loss of the ability to identify familiar objects by touch (with the preservation superficial or deep sensitivity) occurs with lesions of the parietal lobe and is defined as astereognosis or true astereognosis. Loss of the ability to identify familiar objects by touch, caused by the loss of superficial or deep sensory, can be observed at various levels of destruction of sensitive guide and be considered as a false astereognosis. Dysesthesia is characterized by change of sensation perception, for example the appearance of pain in response to simple touch (tactile allodiniya) or touching of cold objects (cold allodiya)

Pain can be classified as nociceptive, non-nociceptive and psychogenic. Nociceptive pain is caused by activation of pain receptors (nociceptors) in response to damage of the skin, skeleto- muscular system and internal organs. It can be felt not only in the place of damage, but also distant regions which innervate those same segments of the spinal cord, that area of damage (synalgia). For example, during acute myocardial ischemia (stenocardia or infarct) pain is often felt not only at the chest, but also in the left arm and jaw.

Neuropathic pain occurs when lesion in sensory conductors; it doesn’t coincide with place of lesion and presents ¬ projection pain. A striking example of projection of pain is phantom pain that occurs after amputation of limbs in the form of unpleasant sensations and the absence of its parts (e.g. ; fingers). The defeat of sensitive conductors can cause paresthesia, hyperesthesia and dysesthesia, which often combined with neuropathic pain.

Pain regard as psychogenic in cases where I n case of nonexistent its organic cause (somatic or neurologic disease) or the character and intensity of pain is clearly inconsistent with an organic lesion. Psychogenic pain usually occurs on the background of depression and anxiety disorders or other psychiatric disorders.

Type (syndrome) of sensory disorders

Depending on the localization of sensory disorders, we can distinguish type (syndrome), which indicates the location and destruction of sensitive conductors and to put a topical diagnosis. Fig. 2 shows the main types of disorders of sensitivity.

Mononeuropathic type sensory disorders, (see Fig. 2, a) manifests as sensory disorders in region of innervations of one nerve and indicate its damage (mononeuropaty). Region of sensory impairment in of one nerve usually considerable lower than zone it anatomically innervates, due to cross-innervation of the skin adjacent nerves. First sensory symptoms are often are pain and parasthesia. Next to them usually is associated loss of sensory in the form monoginestesia or monoanesthesia.

Polyneuropathic type of sensory disorders (see Fig. 2,b) manifest as sensory defect in the distal extremities in type "socks" ( "golf", "stocking"), "gloves" and show lesion of the distal peripheral nerves of limbs (polyneuropathy). The degree of sensory disorders his fingers of limbs and weaker in proximal direction. Sensory disorders were significantly more common in the lower extremities. The lesion of the peripheral nerves of the extremities usually first manifests as pain, paresthesia and hyperesthesia, which is gradually replaced hypoesthesia or anesthesia.

Segmental radicular-type of sensory disorders is sensory defect in the form of horizontal lines on the trunk or vertical lines on the limbs (“stripe" on the leg) and indicates the posterior spinal-cerebral roots (radiculopathy). Pain and paresthesias usually appeared to be first symptom of lesion in spinal cord roots.

Loss of sensory in form of hypesthesia (rarely anesthesia) often is not detected in the all region that the destructed radix innervates butonly in distal parts of limbs because of overlapping in innervations zones by adjacent spinal cord roots/radix.

Segmental-dissociated-type of sensory disorders is characterized by loss of pain and temperature sensation in form of "jacket" or "half jacket” indicating lesions of posterior horns or anterior gray commissure of spinal cordin the level of the respective segments of the spinal cord (in case of "jackets" or "half-jacket" there is a lesion on cervicothoracic segments). Segmental-type sensory disorders occur rarely, the cause more often are syringomyelia or tumour of spinal cord.

Segmental-conductor type of sensory disorders (see Fig. 2. ) manifests as abnormal sensation more distal from the horizontal level of lesion on body. Loss of pain and temperature sensation on the one hand shows lesion in contralateral spinothalamic tract in the lateral funiculus of spinal cord by 1-2 segments above the level of abnormal sensory of the skin. For example, loss of pain and temperature sensation on the left half of body below the 8th thoracic segment and in the left leg indicates lesion of the right lateral funiculus at the level of 6-7th segment of the thoracic segments. The loss of deep sensation on the one hand points to the posterior cord lesion on the same side. Often, the loss of deep sensation occurs only in the lower extremities when it normal in the upper extremities, which indicates that the lesion of both posterior

funiculus of thoracic segments of the spinal cord.

Cerebral type of sensory disorders (see Fig. 2, ) characterized by decrease or loss of sensation on one side of the body with hemihypoesthesa and hemianesthesia and indicate the lesion of sensory conduction of brain on the opposite side. In hemihypoesthesa and hemianesthesia, brain lesion on contralateral side may be at the level of the parietal lobe (postcentral gyrus), corona radiata, internal capsule, thalamus and the first half of the brain stem. Any damage of the thalamus or sensory conduction in other parts of the brain, pain, paraesthesia and hemihypoesteziya is on contralateral side of the body. Pain is of prickling, burning periodically intensified; light touching of skin provoke pain attack. Threshold of pain stimulation perception is increased, but the repeated irritation caused by several period of intense and distressing pain that remains after the application of painful stimuli - hyperpahy. This pain syndrome is defined as "central pain".

Any damage to the brain stem may cause alternating hemianesthesia (see Fig. 2, e) - loss of pain and temperature sensitivity in the face, in the one half of trunk and limbs - contralaterally. This abnormal sensation indicate lesion of caudal part of brain, where trigeminal nerve is located and responsible for sensation odf skin and passes spinothalamic tract

Cortical type of sensory disorders (Fig. 2, g) manifests as abnormal sensation, most often hypoesthesia or paresthesia, only in the region, hands or feet, and shows lesion corresponding parts postcentral gyrus of the parietal lobe of the opposite hemisphere. When the cortical type of localization sensory disorders does not correspond to zones of peripheral innervation, which is feature from mononeuropathy and segmental-radicular-type of sensory disorders.

Disorder may have a sensitivity and psychogenic character. In such cases, the localization of sensitivity defects usually do not correspond to the possible types of disorders of sensitivity arising in organic defect of sensory; and in demonstration of anormal joint-muscular sensation, patient does not have sensitive ataxia, changes in muscle tone and the reflexes. In the examination of sensation with closed eyes, patient in each test (eg. Application ofpain stimuli) responds by saying that he feels nothing and tells us thatsensation is preserved. For hysterical hemihypoestesia, shows characteristic abnormal sensation in one half of the body (usually the left) with the border, along the medial line, differs from organic hemihypoesthesia where the sensory abnormalities have no clear boundaries.

Additional methods of investigation used for objectification of sensory disorders, clarification the localization of lesion and to ascertain the neurological disease. Electroneuromyography (ENMG) allows us to identify signs of lesion in sensory conduction of peripheral nerves, spinal roots. Sensory-triggering potentials investigation allow us to clarify lesion of sensory conductors not only peripheral, but also in spinal and cerebral level. To determine the level of lesions in the brain and spinal cord, neurovisualization methods - computer X-ray and magnetic resonance tomography of the head and spine.

Treatment of sensory disorders – is to treat main disease, if it is possible. In acute pain, and as symptomatic treatment, analgesic may helps. In the case of chronic pain rather than analgesics, drugs is given often in high doses, it is advisable to use antidepressants and antiepileptic. Analgesic effect of antidepressants is not associated directly with their antidepressant effect and appears at about no low doses. Amitriptyline is used as increasing doses (from 10 mg to 75 mg / day) until a positive effect is achieved. You can use other antidepressants such as mianserin (lerivon) from 30-90 mg/day. Antiepileptic especially effective in paroxysmal pain, carbamazepine is used from 200-900 mg/day, clonazepam (antelepsin) for I 4 mg/day, valproic acid by 600-800 mg/day, lamiktal (lamotrigine) for 100-200 mg/day. In addition to medical therapy, we can use physiotherapy, reflex therapy, blockade with local anesthetics and corticosteroids.

TYPES OF SENSORY DISORDERType Localization of Sensory Damage Localization of Lesion

Mononeuropathy In the area of innervations of a nerve Peripheral nerve

Polyneuropathy Distal part of limb, "socks" ("golf") type on the lower limb, "gloves" type on the upper extremities

Distal peripheral nerves

Segmental-radicular

In longitudinal lines form on the trunk or vertical lines on the limbs (“stripe" on the leg)

Posterior spinal cord roots

Segmental-dissociated

Loss of pain and temperature sensitivity in different segments, most often in the form of "jacket" or "half jacket”

The lesion of the posterior horn or anterior gray commissure of spinal cord

Spinal conductionSensory disorder below the horizontal level on the trunk

Lateral and/or posterior spinal cord

Cerebral conductivity

Sensory disorder at half of the head, trunk and legs with one side

Postcentral gyrus, corona radiata, internal capsule or thalamus

Alternating hemihypoestesia

Sensory disorder in half of the face on one side and the other side in trunk and limbs

Half of the brain stem

Cortical Only in limited areas of head, hands or legs Postcentral gyrus of opposite hemisphere

TYPES OF PAINTypes of pain Characteristics of pain

Nociceptive Caused by activation of pain receptors (nociceptors) in response to injury; can feel not only the site of damage, but also in other remote areas (synalgia)

NeuropathicLesion arises in the sensory conduction; does not coincide with the place of lesion and presence of projection pain, often combined with other sensory disorders

PsychogenicNature and intensity of pain clearly does not correspond to organic lesion, often marked by depression or other mental disorders

Syringomyelia

Syringomyelia - a chronic disease of the nervous system , characterized by formation of cavities in central parts of spinal cord and frequently in medulla oblongata (syringobulia). Cavities usually are formed in lower cervical and upper parts of spinal cord. Incidence of syringomyelia is 8 -9 cases in 1000 000 population.Causes of disease are unclear, pathogenesis of disease however, role of obstruction of CSF flow/drainage from 4th ventricle into subarachnoid space, is assumed/ suggested, in which hydrodynamics lead to dilatation/ widening of canalis centralis in SC.

Clinical picture:Begin disease at 25 – 40 yrs old, Males are more often affected than woman.Symptoms develop gradually; first of all usually appear derangement of sensation, weight loss and weakness of small muscles of hand. Characteristics segment – dissociative sensory disturbances in form of <jacket> or <half jacket> - loss of pain and temperature sensation while other types of sensations are normal. In syringobulbia, decrease sensation in facial region is also possible. Rarely derangement of sensation and atrophy develop in lower parts of body and in legs. In consequences of loss of pain sensation, often develop trauma, especially burns, which lead to scarring changes of skin. In many cases, it is observed spontaneous pain, which may be burning, acute or gunshot/ lighting pain.

Mostly early motor derangements are weakness and atrophy of hands muscle. Further, it is possible to extend to peripheral paresis of proximal parts of arms and shoulder girdle; some patients develop central paresis of lower limbs (in consequences of lesion of lateral funiculus of SC).

Not frequently, seen trophic skin changes in hands, in 20% of cases observed arthropathy (often of elbow and shoulder joints). In syringobulbia, may develop paralysis of soft palate, pharynx and larynx, tongue atrophy, vertigo, nystagmus. Patients with syringomyelia usually have dystrophic changes; unproportionate length of arms in relation to body, finger distortion, anomalies of ears, short neck, kyphosis and scoliosis of vertebra etc.

Duration/course of the disease is chronic, slowly progressive. Sudden intensification of symptoms happen due to physical exercise, trauma or develop in bleeding/ hemorrhage into syringomyelic cavity.In syringobulbia, possible disturbances in respiration due to stridor of larynx; (obstruction) combined with bronchopulmonary complications, which may bring to lethal outcome. However, in most patients, disease doesn’t shorten duration of life and they, as a rule, maintain working capacity for a long time.

Diagnosis: Leading importance: MRI of SC. MRI allows to visualize cavity inside SC and exclude other diseases. EMG (electromyography) – clarity lesion of anterior horn of SC on cervical level; characteristic of syringomyelia.

Treatment: Recommend to be careful of damage injury to skin surface, recommended medical gymnastics (physical trainings) and massage. In long and intense pain, prescribe analgesics and antidepressants. Whenbig syringomyelic cavity forms, operative drainage and shunting maybe effective to be done.