Fifth Stage
Internal Medicine
Dr. Abbas / Lec . 6
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Sensory Pathways and Pain
Peripheral nerves and spinal roots
Peripheral nerves carry all modalities of sensation from either free or specialized
nerve endings to dorsal root ganglia and thus to the cord
Lesions Of The Sensory Pathways
Altered sensation (paraesthesia), tingling, clumsiness, numbness and pain are
the principal symptoms of sensory lesions. The pattern usually suggests the
site of pathology.
Peripheral nerve lesions
Section of a sensory nerve is followed by complete sensory loss
Nerve entrapment causes numbness, pain and tingling. Tapping the site of
compression sometimes causes a sharp, electric-shock-like pain in the
distribution of the nerve, e.g. Tinel's sign in carpal tunnel syndrome
Neuralgia refers to local pain of great severity in the distribution of a damaged
nerve. Examples are:
trigeminal neuralgia postherpetic neuralgia)
Spinal root lesions
(Root pain)
The pain of root compression is felt in the myotome supplied by that root, and
there is also a tingling discomfort in the dermatome. The pain is made worse by
manoeuvres that either stretch the nerve root (e.g. limitation of straight
leg raising in lumbar disc prolapse) or increase pressure in the spinal
subarachnoid space (coughing and straining
Spinal cord lesions
Transverse lesion of the spinal cord produce loss of all modalities below that
segmental level,. If the transverse lesion is vascular in origin (e.g. due to
anterior spinal artery thrombosis), the posterior one-third of the spinal cord (and
therefore the dorsal column modalities) may be spared
Lesions damaging one side of the spinal cord will produce sensory loss for
spinothalamic modalities (pain and temperature) on the opposite side and for
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dorsal column modalities (joint position and vibration) on the same side as the
lesion. This is the pattern seen in the Brown-Séquard syndrome
Lesions in the centre of the spinal cord (e.g. syringomyelia,) spare the
dorsal columns but affect the spinothalamic fibres crossing the cord from both
sides over the length of the lesion. The sensory loss is therefore dissociated (in
terms of the modalities affected)
Pontine lesions
Since lesions in the pons (e.g. an MS plaque) lie above the decussation of the
posterior columns,
and the medial lemniscus and spinothalamic tracts are close together, there is
loss of all forms of sensation on the side opposite the lesion.
Thalamic lesions
Thalamic pain, also called thalamic syndrome, usually follows a small
thalamic infarct. A patient has a stroke (hemiparesis and sensory loss). The
weakness recovers partially or completely but there develops constant very
severe deep-seated burning pain in the paretic limbs. This continues
night and day. Extreme anguish is usual and the secondary depression
may lead to suicide. Thalamic lesions may also produce loss of sensation on
the opposite side of the body; this is a less usual clinical picture
Parietal cortex lesions
Sensory loss, neglect of one side, apraxia and subtle disorders of sensation
occur. Pain is not a feature of destructive cortical lesions. Irritative
phenomena (e.g. partial sensory seizures from a glioma) arising in the parietal
cortex cause tingling sensations in a limb, or elsewhere.
Regional Cerebral Dysfunction:
Higher Mental Functions
Focal lesions of the cerebral cortex,, cause symptoms and signs by two processes:
1--
Suppression or destruction of neurons and surrounding structures
( most common
process - part of the system fails to work.
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2--
Synchronous discharge of neurons by irritative lesions
, e.g. cerebral cortex lesions
cause epilepsy, either partial or generalized.
Frontal lobe
Function
Personality
Emotional control
Social behavior
Contra lateral motor control
Language
Micturition Disinhibition
Dysfunction
Lack of initiation
Antisocial behavior
Impaired memory
Expressive dysphasia
Incontinence ,Impaired smell
Contra lateral hemi paresis
Frontal release signs1Versive seizures
Focal motor seizures (Jacksonian march)
Continuous partial seizures (epilepsia partialis continua)
Dominant parietal lobe
Function
Language
Calculation
Dysfunction
Dysphasia
Contra lateral hemisensoryloss
Focal sensory seizures
Dyscalculia Astereognosis Dyslexia Agraphaesthesia Apraxia
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Non-dominant parietal lobe
Function
Spatial orientation
Constructional skills
Dysfunction
Neglect of contra lateral side
Contra lateral hemi sensory loss
Astereognosis
Focal sensory seizures
Spatial disorientation
Agraphaesthesia
Constructional apraxia
Temporal: dominant
Function
Auditory perception
Language
Verbal memory
Smell
Balance
Dysfunction
Receptive aphasia
Dyslexia
Impaired verbal memory
Contra lateral homonymous upper quadrantanopia
Complex hallucinations (smell, sound, vision, memory)
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Temporal: non-dominant
Function
Auditory perception
Melody/pitch perception
Non-verbal memory
Smell
Balance
Dysfunction
Impaired non-verbal memory
Impaired musical skills (tonal perception)
Contra lateral homonymous upper quadrantanopia
Complex hallucinations (smell, sound, vision, memory)
Occipital
Visual processing
Dysfunction
Visual inattention
Visual loss
Visual agnosia
Homonymous hemianopia (macular sparing)
Simple visual hallucinations (e.g. phosphenes, zigzag lines)
Thank you,,,