Thalamic Pain Syndrome, Ataxia, and Peripheral Neuropathy PDF

# Thalamic Pain Syndrome - Also known as central post stroke pain (CPSP) - Rare condition that develops after infarction of ventro-postero-lateral thalamus. - The Patient presents with: - Contralateral sensory loss. - Hemi-ataxia. - Thalamic pain: spontaneous bursts of intolerable burni...

# Thalamic Pain Syndrome - Also known as central post stroke pain (CPSP) - Rare condition that develops after infarction of ventro-postero-lateral thalamus. - The Patient presents with: - Contralateral sensory loss. - Hemi-ataxia. - Thalamic pain: spontaneous bursts of intolerable burning pain sensation (accompanied by 2ry hyperalgesia and allodynia (discussed earlier) # Ataxia - Incoordination of voluntary movements without paralysis - Types of ataxia: - Sensory ataxia: Due to loss of position sensation as in tabes dorsalis or pernicious anemia which cause destruction of posterior column. - Cerebellar ataxia: due to lesion in neocerebellum. - Vestibular ataxia: due to lesion in the Vestibular division of the 8th nerve. # Peripheral Neuropathy - Mononeuropathy: Injury or lesion of one peripheral nerve leads to loss of all sensations in the area supplied by this nerve. - Polyneuropathy (peripheral neuritis): - Diffuse lesion of all peripheral nerves, as in case of Vitamin B12 deficiency or diabetic neuritis. - Affects the peripheral ends of sensory nerves at the distal parts of the limbs leading to "glove and stocking" sensory disturbance (numbness, tingling, burning then total sensory loss). - Injury / damage to a peripheral nerve can lead to chronic neuropathic pain # Herpes Zoster - Viral infection, in which the herpes virus attacks a dorsal root ganglion (DRG) in patients with history of varicella (chicken pox) infection. - Virus starts to reproduce causing irritation of pain afferents in the DRG leading to severe pain felt in dermatomal segment supplied by the infected ganglion. - The virus also migrates with neuronal cytoplasmic flow towards the peripheral axons to their cutaneous terminals, where it reproduces leading to painful skin rash and vesicular formation. # Neuropathic Pain - Chronic type of pain occurring due to damage to or pathological changes in nerve fibers either in the peripheral or central nervous system. - Characters: - It is often described as burning, electric, tingling or shooting pain. - It characterized by occurring in bouts or paroxysms. - It is usually accompanied by hyperalgesia and/or parasthesia. - Examples: - Trigeminal neuralgia: is a unilateral facial pain confined to areas supplied by the 2nd and 3rd divisions of the trigeminal nerve. - Herpes zoster. - Diabetic neuropathy. - Sciatica. # Sensory Cortical Lesions - Lesion in the somatic sensory area SSI: Somatic sensations are not abolished. However, here is loss of the following types from the opposite side of the body: - Fine touch, Stereognosis and Proprioceptive sensations. - Discrimination of mild grades of weights and temperature. - Localization of the source of sensations. - Pain localization, but pain sensation is least affected. - Lesion in the somatic sensory association cortex: - Astereognosis: The patient loses the ability to correlate shape, size, texture and weight f objects with previous experience. - Amorphosynthesis (Neglect syndrome): The patient neglects contralateral side of his # Syringomyelia - Widening of the central canal by a fluid-filled cavity (or syrinx) in the spinal cord. - This leads to damage of pain and temperature fibers crossing immediately in front of the central canal first. Later, crude touch is affected. - The lesion is bilateral and usually affects the cervical region leading to "jacket" loss of pain and temperature sensations. - Dorsal column sensations remain intact (fine touch is intact) and the condition is described as dissociated sensory loss # Tabes Dorsalis - Neurosyphilitic disease that causes slow degeneration of the sensory nerves in dorsal root and dorsal column mostly in the lumbosacral spinal cord leading to: - Irritation of pain fibers and attacks of severe pain, followed by: - Degeneration and Atrophy of the Dorsal Column leading to: - Loss of vibration sense. - Loss of proprioceptive sensation leads to incoordination of voluntary movements known as "Ataxia". - Sensory ataxia is characterized by high steppage (or stamping) gait and +ve Romberg's sign (patient can't maintain his erect position with closed eyes). # Hyperalgesia - Exaggerated pain response: - Primary hyperalgesia: - occurs in the injured or inflamed skin area - caused by sensitization of peripheral nociceptors by inflammatory mediators, - thus there is lowered threshold of pain e.g. in sunburned skin. - Secondary hyperalgesia: - occurs in uninjured skin - due to sensitization of the central neurons of pain. - The pain threshold is increased, but when reached, the pain produced is prolonged, severe and intolerable. - This may be accompanied by allodynia (exaggerated pain response to non- painful stimuli).e.g. Thalamic pain # Spinal cord Hemi section (Brown Sequard syndrome) - Hemi section of the spinal cord results in the following manifestations: - At the level of lesion: On the same side: - Sensory: Loss of all sensations at dermatome supplied by that posterior root entering at the site of injury - Motor: Flaccid paralysis (lower motor neuron lesion) and loss of all reflexes - Below the level of lesion: - On the same side: - Sensory: Lesion to dorsal column leads to loss of all sensations carried by it (fine touch, pressure, vibration, sense of position and of movement). - Motor: Lesion to corticospinal tract leads to spastic paralysis (upper motor neuron lesion), hyper-reflexia and +ve Babiniski. - On the opposite side: - Sensory: loss of pain and temperature (Lesion to crossed spinothalamic tract), touch is not lost but decreased on both sides. - Motor: no effect # Cerebellum Function in Voluntary Movements - The lateral zones of the cerebellum receive afferent impulses from cortical association areas, which are believed to be the site of origin of commands for voluntary movements. - It seems that these impulses are transmitted into the cerebellum, which, with other areas of CNS, plans movements. - The cerebellum then sends efferent signals to the motor area of the cerebral cortex, and the movement is initiated via the corticospinal tract. - The ability to progress smoothly from one movement to the next depends on the fact that lateral cerebellum plans for next movement at the same time the present movement is occurring. - The lateral cerebellum also provides appropriate timing for each movement. Thus, lesion to these zones leads to inability to judge the distance moved by a particular part in a given time. # Cerebellar Lesions - Ataxia: - Pronounced abnormality appears when the patient moves. - Although there is neither paralysis nor sensory deficit all, movements are characterized by marked ataxia. - Ataxia is defined as incoordination of movements due to errors in the rate, range, force and direction of movement. - If only the cortex of the cerebellum is involved, the movement abnormalities gradually disappear as compensation occurs. - Lesion of the cerebellar nuclei produce more generalized defects and the abnormalities are permanent. # Stretch Reflex Abnormalities - Areflexia: - Interruption of reflex arc in: - Peripheral neuritis. - Tabes dorsalis. - Poliomyelitis - Hypereflexia: - Interruption of inhibitory impulses in: - Upper motor neuron lesion - Anxiety. - Hyperthyroidism - Hyporeflexia: - Interruption of facilitatory impulses in: - Neocerebellar syndrome - Sleep - myxoedema # Cerebellum Function in Voluntary Movements (cont.) - Servo- comparator Function: - The motor areas of cerebral cortex on one side are connected to the intermediate zone of cerebellar hemisphere of opposite side by a closed feedback circuit (Cortico-Ponto-cerebello-thalamo-cortical). - When the motor cortex, transmits a signal to a group of muscle (via pyramidal and extrapyramidal tracts) to execute a particular movement, it transmits same information simultaneously to intermediate zone of the cerebellum through the "Cortico-Ponto-cerebellar tract" to inform cerebellum about the order given from cortex to muscles. - As the muscles respond to cortical signals by contraction, receptors such as muscle spindles, respond by transmitting signals upwards along spino cerebellar tract to cerebellum. - The intermediate zone of cerebellum compares intended movements with actual movements, deep nuclear cells of interposed nucleus initiates corrective signals, which are sent to the motor cortex via "cerebello -thalamo-cortical tract". # Cerebellar Lesions (cont.) - Other manifestations: - Disturbance of posture and gait: head is tilted to the side of the lesion. The patient has a wide-based, unsteady drunken gait. The patient also tends to fall to the side of the lesion. - Slurred or scanning speech: Is due to defects of skilled movements involved in production of speech. - Dysmetria or past-pointing: Other voluntary movements are also highly abnormal e.g. attempting to touch an object with a finger results in overshooting to one side or the other. This is tested by finger - nose test. - Intention tremor : Dysmetria, initiates a gross correction action, but correction overshoot to other side. Consequently, finger oscillates back and forth causing tremors. It is called kinetic tremors, and is absent at rest and appears during voluntary action. - Rebound phenomenon: inability to "put on" the brake i.e. to stop movement promptly. Normally, flexion of forearm against resistance is quickly checked when resistance force is suddenly broken off. The patient with cerebellar disease can not brake movement of limb, and the forearm flies backward in a wide arc. - Adiadochokinesia: inability to perform rapidly alternating opposite movements such as repeated pronation and supination of the hands. - Decomposition of movements: Patients with cerebellar disease have difficulty performing actions that involve simultaneous motion at more than one joint. It is tested by heel-knee test. - Nystagmus: This is tremor of the eye ball, which occurs when the patient attempts to fix his gaze on an object to the side of his head (Horizontal nystagmus). It is due to absence of damping function. - Hypotonia: There is marked hypotonia on the side of the lesion due to marked decrease of facilitatory effect of cerebellum on stretch reflex. When the knee jerk is elicited, it is reduced and pendular # Cerebellum Functions - Functions in voluntary movements: - Servo- comparator function. - The braking effect of the cerebellum. - Planning and timing function of the cerebellum - Other functions: - Function of the cerebellum in equilibrium. - Function of the cerebellum in muscle tone. # Muscle Spindle Role in Muscle Tone - Muscle tone is continuous, alternating, reflex, subtetanic contraction of muscle fibers. It may also be define as resistance of the muscle to stretch. - Base of muscle tone: Static stretch reflex - During rest the muscle spindle is continuously stretched because: - Length of skeletal muscle is shorter than distance between its origin & insertion. - Attractive force of earth's gravity. - Continuous y-efferent discharge under normal conditions. - Muscle tone does not cause fatigue because - It is due to alternate contraction of different muscle fibers. - Contraction is subtetanic. - Muscle fibers involved in muscle tone are red muscle fibers, which contract slowly. - Functions of muscle tone - Maintain body posture against the effect of gravity. - Provides a background for voluntary movements. - Helps in regulation of body temperature. # Cerebellum Function in Equilibrium - The flocculondular lobe in the cerebellum is the site which plays an important role in the maintenance of equilibrium. - It is connected by a feedback circuit with the vestibular apparatus. - Inputs from the vestibular apparatus are used by the cerebellum and send output signals→ brain stem reticulospinal & vestibulospinal tracts maintain equilibrium through changes in tone of axial and girdle muscles. - Damage to the flocculonodular lobe leads to disturbance of equilibrium. # Cerebellar Lesions (cont.) - Cause: is due to damage of the deep cerebellar nuclei as well as the cerebellar cortex. - Manifestations occur on the same side of the lesion i.e. a lesion of the left cerebellar hemisphere produces its effects on the left side of the body. - Ataxia: - Other manifestations : - Disturbance of posture and gait - Dysmetria or past-pointing - Intention tremor (kinetic tremors) - Adiadochokinesia - Slurred or scanning speech - Decomposition of movements - Nystagmus - Rebound phenomenon - Hypotonia # Stretch Reflex Significance - Helps to maintain the muscle length. - Control of voluntary movements. - Muscle tone. # Cerebellum Function in Muscle Tone (cont.) - The neocerebellum is facilitatory to the stretch reflex. - Since its feedback time is longer than the simple cord stretch reflex, it prolongs the effect. - This helps further in the maintenance of posture. - Meanwhile, the paleocerebellum is inhibitory to muscle tone, through the inhibitory reticular formation. # Muscle Spindle Role in Control of Voluntary Movements - Servo-Assistant function during muscle contraction "α-γ- linkage" - Descending impulses from higher centers stimulate both alpha and gamma motor neurons simultaneously. Spindle remains capable of reflexly adjusting motor neuron discharge throughout contraction. - Damping function: Smoothen muscle contraction. - During movements, motor signals are transmitted from cortex through pyramidal tract to AHC in an unsmooth form, resulting in an oscillatory (jerky) movement. Stretch reflex prevents this oscillation and smoothen muscle contraction. - Prove: Cutting sensory nerve (de-affrenation) loss of stretch reflex→ un-smooth jerky contraction. # Cerebellum Function in Voluntary Movements (cont.) - The braking effect of the cerebellum - Cerebellum must act to inhibit the motor cortex at the appropriate time after the muscles have begun to move. - The cerebellum assesses the rate of movement, calculates the length of time needed to reach the intended point and then transmits inhibitory impulses to the motor cortex to inhibit the agonist and excite the antagonist muscles. - Thus, brakes are applied to stop the movements at the precise intended point. # Stretch Reflex Significance (cont.) - Helps to maintain the muscle length. - Control of voluntary movements. - Muscle tone.