Neurology Quiz 3

(Ref: Harrison 20th p 2073; Harrison 19th page 1775)
Alpha rhythm has discharge frequency of 8-13 Hz. On eye opening the pattern changes to beta rhythm. In pontine or diffuse cortical anoxia a special pattern of alpha coma is defined by widespread alpha rhythm that resembles the normal rhythm but does not alter on environmental stimuli.

(Ref: Goodman gilman 12th ed., pg 748)
• Mannitol, a 6-carbon sugar and an osmotic diuretic and can have significant beneficial effects on ICP, cerebral blood flow and brain metabolism.
Mannitol has two main mechanisms of action. Immediately after bolus administration it expands circulating volume, decreases blood viscosity and therefore increases cerebral blood flow and cerebral oxygen delivery.
Its osmotic properties take effect in 15-30 minutes when it sets up an osmotic gradient and draws water out of neurons.
However after prolonged administration (continuous infusion). mannitol molecules move across into the cerebral interstitial space and may exacerbate cerebral oedema and raise ICP
Mannitol itself directly contributes to this breakdown of the blood brain barrier.
Mannitol is therefore best used by bolus administration where an acute reduction in ICP is necessary. For example the patient with signs of impending herniation unilateral dilated pupil / extensor posturing) or with an expanding mass lesion may benefit from mannitol to acutely reduce ICP during the time necessary for CT scanning and/or operation.
Mannitol is wholly excreted in the urine and causes a rise in serum and urine osmolality. Patients with poor renal perfusion (shock), sepsis, receiving nephrotoxic drugs or with a serum osmolality over 320mOsm are at risk of acute a tubular necrosis. Hypovolemia should be avoided with the infusion of isotonic fluids as necessary.

(Ref: Harrison 20th p 2084; Harrison 19th p 1785)
The clinical picture is of a patient of a subarachnoid hemorrhage with a probable "warning leak”.
• Subarachnoid hemorrhage has a characteristic clinical picture. Its onset is with sudden headache of a severity never experienced previously by the patient. This may be followed by nausea and vomiting and by a loss or impairment of consciousness that can either be transient or progress inexorably to deepening coma and death.
If consciousness is regained, the patient is often confused and irritable and may show other symptoms of an altered mental status. Neurologic examination generally reveals nuchal rigidity and other signs of meningeal irritation, except in deeply comatose patients.
Occasional patients with aneurysms have headaches, sometimes accompanied by nausea and neck stiffness, a few hours or days before massive subarachnoid hemorrhage occurs. This has been attributed to "warning leaks” of a small amount of blood from the aneurysm.
A CT scan (preferably with CT angiography) should be performed immediately to confirm that hemorrhage has occurred and to search for clues regarding its source. CT in dings sometimes are normal in patients with suspected hemorrhage, and the cerebrospinal fluid must then be mined for the presence of blood or xanthochromia before possibility of subarachnoid hemorrhage is discounted.

(Ref: Harrison 20th p 2072; Harrison 19th p 1775)
Ocular bobbing is a jerky downward deviation of the eyes with slow return, seen in comatose patients and believed to be due to a pontine lesion.
Ocular dipping is inverse of ocular bobbing and slow downward deviation with fast upward movement and occurs due to diffuse cortical suppression in patients of cerebral anoxia like after CPR.
Damage to medial longitudinal fasiculus leads to ataxic nystagmus.
Severe refractive errors or macular disease will lead to pendular nystagmus
Downbeat nystagmus is seen with cerebellar lesions.
Upbeat nystagmus with brainstem lesions

(Ref: Harrison 20th p 3068; Harrison 19th p 2568)
The following signs may be present in patients with T.I.A:
• Ocular dysmotility and Amaurosis fugax
• Forehead wrinkling asymmetry
• Incomplete eyelid closure
• Asymmetrical mouth retraction
• Loss of the naso-labial crease
• Swallowing difficulty
• Lateral tongue movement
• Weak shoulder shrugging
• Visual field deficits
The cerebellar system can be tested by assessing ocular movement, gait, and finger-to-nose and heel-to-knee movements, with an eye to signs of past-pointing and dystaxia, hypotonia, overshooting, gait dystaxia, and nystagmus

(Ref. Harrison 20th P 3071; Harrison 19th p 2572)
The patient has an embolic stroke due to athero-sclerosis secondary to diabetes. The anterior circulation damage causes pure motor paralysis without sensory deficit. The blood vessel causing such deficit is lenticulo-striate artery which is the branch of the largest blood vessel in the brain ie middle cerebral artery.