Neurology- Sensory System Flashcards
1
Q
What is the sensory system
A
- the sensory system comprises the simple sensations of light, touch, pain, temp and vibration
- together with joint proprioception and higher cortical sensations, which include 2-point discrimination, stereognosis (tactile recognition), graphaesthesia (identification of letters or numbers or number traced on the skin) and localisation
- detailed examination of sensation is time-consuming and unnecessary unless the patient volunteers sensory symptoms or suspects particular pathology (SCC or mononeuropathy)
- in patients without sensory symptoms, assessing light touch only of all four limbs as a screening process with suffice
- it is useful to have a working knowledge of how the dermatomal distribution and the sensory distribution of the more commonly entrapped peripheral nerves
2
Q
Sensory system- anatomy
A
- proprioception and vibration are conveyed in large, myelinated fast-conducting fibres in the peripheral nerves and in the posterior (dorsal) columns of the spinal cord
- pain and temperature sensation are carried by small, slow-conducting fibres of the peripheral nerves and the spinothalamic tract of the cord
- the posterior column remains ipsilateral from the point of entry upto the medulla, but most pain and temperature fibres cross to spinothalamic tract with one or 2 segments of entry in the cord
- all sensory fibres relay in the thalamus before sending info to the sensory cortex
3
Q
Sensory sensation- common presenting symptoms
A
- sensory symptoms are common, and it is important to discern what the patient is describing
- clarify numbness is a lack of sensation rather than weakness or clumsiness
- ## neuropathic pain (pain due to disease or dysfunction of the PNS or CNS) is often severe and refractory to simple analgesia
4
Q
Sensory symptoms are defined as follows
A
- paraesthesia: tingling or pins and needles
- dysaesthesia: unpleasant paraesthesia
- hypoaesthesia: reduced sensation to a normal stimulus
- analgesia: numbness or loss of sensation
- hyperaesthesia: increased sensitivity to a stimulus
- Allodynia: painful sensation resulting from non-painful stimulus
- hyperalgesia: increased sensitivity to a painful stimulus
5
Q
Sensory symptoms- examination
A
- The aim is to focus on the exam
- look for a sensory level of the history and exam suggest spinal cord pathology
- a glove and stocking pattern usually starting distantly, caused by a peripheral neuropathy, or sensory disturbance in a specific nerve territory
- be guided by the history and the exam findings from the motor system and reflexes
- it is useful to ask the patient to map out their areas of sensory disturbance if they can
6
Q
Sensory symptoms- light touch
A
- while the patient looks away or closes their eyes, use a wisp of cotton wool (or finger) and ask the patient to say yes to each touch
- time the stimuli irregularly and make a dabbing rather than a striking or ticking stimulus
7
Q
Sensory symptoms- superficial pain
A
- use a fresh neurological pin, not a hypodermic needle
- explain and demonstrate that the ability of sharp pinprick is being tested
- map out the boundaries of any area of reduced, absent or increased sensation
- ## move from reduced to higher sensibility that is, from hypoaesthesia to normal or normal to hyperaesthesia
8
Q
Temperature
A
- touch a patient with a cold metallic object and ask if it feels cold
- more sensitive assessment requires tubes of hot and cold water at controlled temperatures, but this is seldom performed
9
Q
Sensory modalities
A
- in addition to the modalities conveyed in the principal ascending pathways (touch, pain, temperature, vibration and joint position), sensory examination includes tests of discrimination aspects of sensation, which may be impaired by lesions of the sensory cortex
- assess these cortical sensory functions only if the main pathway sensations are intact.
- consider abnormalities on sensory testing according to whether the lesion is in the peripheral nerves, dorsal roots or spinal cord or is intracranial.
10
Q
Peripheral nerve and dorsal roots
A
- many diseases affect peripheral nerves, generally peripheral neuropathies or polyneuropathies
- peripheral neuropathies tend to affect lower limbs starting with the toes
- upper limbs often become involved once the Sx extend beyond the knees
- Sx first affecting the upper limbs suggest demyelinating rather than animal neuropathies or disease of the nerve roots or spinal cord
- in many cases, touch and pinprick sensations are lost in stocking and glove distribution
- there may be autonomic dysfunction (sweating, sphincter control, orthostatic drops)
- in large neuropathies (e.g. Guillian-barre), vibration and joint position may be affected
- patients may stagger when eyes are closed (Romberg’s sign)
11
Q
Spinal cord
A
- traumatic and compressive spinal cord lesions cause loss or impairment of sensation in a dermatological distribution below the lesion
- a zone hyperaesthesia may be found in dermatomes immediately above the level of sensory loss.
- syringomyelia (fluid filled cavity within the spinal cord) can result in altered spinothalamic (pain and temp) sensations and motor function
- when 1/2 of the cord is damaged, brown-Séquard syndrome may occur
- this is characterised by ipsilateral upper motor neuron weakness and loss of touch, vibration and joint position sense with loss of pain and temperature
12
Q
Intracranial lesions
A
- brainstem lesions are often vascular, and you must understand the relevant anatomy to determine the sort of the lesion
- lower brainstem lesions may cause ipsilateral numbness in one side of the face (V nerve) and contralateral numbness (spinothalamic tract)
- thalamus lesions may cause patchy sensory impairment in the opposite side with unpleasant, poorly localised pain, often of a burning quality
- cortical parietal lobe lesions typically cause sensory inattention but may also affect joint position sense, 2 point discrimination and steroneogenesis (tactile)
