SENSORY LESION By Prof. ASHRAF HUSAIN

Sensory Pathway Lesions

A. Dorsal column syndrome includes the fasciculi gracilis (T6–S5) and cuneatus (C2–T6) and the dorsal roots. is seen in subacute as tabes dorsalis combined degeneration (vitamin B12 neuropathy). is seen in neurosyphilis as and in nonsyphilitic sensory neuropathies.

A. Dorsal column syndrome (contd) results in the following ipsilateral sensory deficits found below the lesion: 1)loss of tactile discrimination 2)loss of position and vibratory sensation 3)astereognosis 4) sensory loss 5)paraesthesia and pain (dorsal root irritation) 6) hyporeflexia (due todorsal root deafferentation) 7) urinary incontinence, constipation and impotence (due todorsal root deafferentation) 8) romberg sign (sensory dystaxia) (standing patient is more unsteady with eyes closed)

B. Lateral spinothalamic tract lesion results in contralateral loss of pain and temperature sensation one segment below the level of the lesion.

C. Ventral spinothalamic tract lesion results in contralateral loss of light (crude) touch sensation three or four segments below the level of the lesion. does not appreciably reduce touch sensation if the dorsal columns are intact

D. Dorsal spinocerebellar tract lesion results in ipsilateral leg dystaxia; patient has difficulty performing the heel-to-shin test.

E. Ventral spinocerebellar tract lesion results in contralateral leg dystaxia; patient has difficulty performing the heel-to-shin test.

Peripheral Nervous System Lesions may be sensory, motor, or combined. affect spinal roots, dorsal root ganglia, and peripheral nerves

A. Herpes zoster (shingles) is a common viral infection of the nervous system. consists of an acute inflammatory reaction in the dorsal root or cranial nerve ganglia. is usually limited to the territory of one dermatome; the most common sites are T5 to T10. causes irritation of dorsal root ganglion cells, resulting in pain, itching, and burning sensations in the involved dermatomes. produces the characteristic vesicular eruption in the affected dermatome.

B. Acute idiopathic polyneuritis (Guillain-Barré syndrome) is also called postinfectious polyneuritis. usually follows an infectious illness. results from a cell-mediated immunologic reaction directed at peripheral nerves. affects primarily motor fibers and causes segmental demyelination and wallerian degeneration. produces LMN(muscle weakness, flaccid paralysis, and areflexia).

B. Acute idiopathic polyneuritis (Guillain-Barré syndrome) contd. results in symmetric paralysis that begins in the lower extremities and ascends to involve the trunk and upper extremities; the facial nerve frequently is involved bilaterally. elevates cerebrospinal fluid (CSF) protein; however, the CSF cell count remains normal.

Figure Sensory homunculus illustrating somatotopic organisation of the primary somatosensory cortex. Downloaded from: StudentConsult (on 8 November :52 PM) © 2005 Elsevier

Parietal lobe lesions, Left parietal lobe lesions cause: partial seizures - paroxysmal attacks of abnormal sensations, spreading down the contralateral side of the body (sensory seizures) sensory/motor deficit - a contralateral hemisensory loss and inferior visual field loss Psychological deficit - an inability to name objects (anomia) and a loss of literacy, with inability to read (alexia), to write (agraphia) and to calculate (acalculia).

Right parietal lobe lesions cause partial seizures - paroxysmal attacks of sensory disturbance affecting the contralateral side of the body (simple sensory seizures) sensory/motor deficit - contralateral hemisensory loss and an inferior visual field loss psychological deficit - an inability to copy and construct designs because of spatial disorientation (constructional apraxia).