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Medicine

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Neurology

Question
24 out of 25
 

Onion bulb appearance on nerve biopsy is seen in: (AIIMS Nov 2010)


A Amyloid neuropathy
B Diabetic neuropathy

C CIDP
D leprosy neuritis

Ans. C

CIDP

Features

Demyelinating neuropathy

Axonal neuropathy

Primary pathology.

Dysfunction of Schwann cells or the myelin sheath.

Destruction of the axon with possible secondary disintegration of the myelin.

Process

Usually segmental

Whole axon involved

Microscopic findings

Sequential episodes of demyelination and remyelination resulting in onion bulb appearance, new myelinated internodes shorter and thinner (seen best on teased nerve preparation.)

Wallerian degeneration:

Break down and phagocytosis of axon and its myelin sheath (myelin ovoids), a regenerating cluster at the proximal stumps.

Examples.

i. Guillain-Barre syndrome

ii. lead toxicity

iii. diphtheria neuropathy

Toxic, metabolic neuropathies many hereditary neuropathies.

Autonomic Neuropathy

Autonomic Testing (Ref. Hari-18th ed., pg- 3355)

1). Heart Rate Variation with Deep Breathing

a. This is a test of the parasympathetic component of cardiovascular reflexes, via the vagus nerve.

b. The lower limit of normal heart rate variation with deep breathing in persons <20 years is >15–20 beats/min, but for persons over age 60 it is 5–8 beats/min.

c. Heart rate variation with deep breathing (respiratory sinus arrhythmia) is abolished by the muscarinic acetylcholine (ACh)-receptor antagonist atropine but is unaffected by sympathetic postganglionic blockade (e.g., propranolol).

2). Valsalva Response

a. This response assesses integrity of the baroreflex control of heart rate (parasympathetic) and BP (adrenergic).

b. Under normal conditions, increases in BP at the carotid bulb trigger a reduction in heart rate (increased vagal tone), and decreases in BP trigger an increase in heart rate (reduced vagal tone).

c. The Valsalva response is tested in the supine position.

d. Autonomic function during the Valsalva maneuver can be measured using beat-to-beat blood pressure or heart rate changes.

e. The Valsalva ratio is defined as the maximum phase II tachycardia divided by the minimum phase IV bradycardia.

f. The ratio reflects the integrity of the entire baroreceptor reflex arc and of sympathetic efferents to blood vessels.

3). Sudomotor Function

a. Sweating is induced by release of ACh from sympathetic postganglionic fibers.

b. The quantitative sudomotor axon reflex test (QSART) is a measure of regional autonomic function mediated by ACh-induced sweating.

4). Orthostatic BP Recordings

a. Beat-to-beat BP measurements determined in supine, 70° tilt, and tilt-back positions are useful to quantitate orthostatic failure of BP control.

b. Allow a 20-min period of rest in the supine position before assessing changes in BP during tilting.

c. The BP change combined with heart rate monitoring is useful for the evaluation of patients with suspected OH or unexplained syncope.

5). Tilt Table Testing for Syncope

The great majority of patients with syncope do not have autonomic failure. Tilt table testing can be used to make the diagnosis of vasovagal syncope with sensitivity, specificity, and reproducibility.

Neurology Flashcard List

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