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A 45 year old woman, presenting with the history of diplopia and dysphagia worsening as the day progresses, can be diagnosed to have: (AIIMS Nov 2010)

A Thyrotoxicosis

B Myasthenia gravis

C Muscular dystrophy

D Brain tumor

Ans. B

Myasthenia gravis

Disorders Of The Neuromuscular Junction (Myasthenia gravis)

1). Etiology. Antibodies directed against the acetylcholine receptor on the motor end plate cause an increased rate of receptor destruction and lead to weakness.

2). Clinical signs. Patients are often young women or older men.

a. Complaints of fatigue in the evening time, double vision, difficulty swallowing and speaking, and limb weakness are common, snarling face appearance. Deep tendon reflexes are normal.

b. On examination, ptosis, bilateral eye movement abnormalities, and proximal weakness may be seen. Cranial nerve involved are 3, 4, 6, 9, 10, 12).

c. Bulbar palsy is common in MuSK antibody positive MG.

d. In MG

i. Pupillary & accommodation reactions are normal

ii. Proptosis is not feature.

e. A thymoma is present in 10%-25% of cases.

f. CPK levels are typically normal.

Extra Edge: Cranial nerve which is not involve is 5th Nerve.

Cogan’s Lid Twitch sign - pt. looks down for 10-20 seconds and then rapidly looks upto primary position, the upper lids often overshoot (retract) and then settle back into a stable position or drift downward. This sign demonstrate fatigability (Fluctuating weakness), which is characteristic of myasthenia.

Useful clinical Tests to assess the effect of treatment.

1). Forward arm abduction

2). Range of eye movement

3). FVC

4). Time of development of ptosis on upward eye movement

Table: Drugs with Interactions in Myasthenia Gravis (MG) ( Ref. Hari-18th ed., pg- 3486, table 386.4)

1). Drugs That May Exacerbate MG

a. Antibiotics

i. Aminoglycosides: e.g., streptomycin, tobramycin, kanamycin (AIIMS May 09)

ii. Quinolones: e.g., ciprofloxacin, levofloxacin, ofloxacin, gatifloxacin

iii. Macrolides: e.g., erythromycin, azithromycin, telithromycin

b. Nondepolarizing muscle relaxants for surgery, D-Tubocurarine, pancuronium, vecuronium, atracurium

c. Beta-blocking agents, Propranolol, atenolol, metoprolol

d. Local anesthetics and related agents, Procaine, Xylocaine in large amounts, Procainamide (for arrhythmias)

e. Botulinum toxin, Botox exacerbates weakness

f. Quinine derivatives, Quinine, quinidine, chloroquine, mefloquine (Lariam)

g. Magnesium, Decreases ACh release

I. Penicillamine, May cause MG

2). Drugs with Important Interactions in MG

a. Cyclosporine, Broad range of drug interactions, which may raise or lower cyclosporine levels.

b. Azathioprine, Avoid allopurinol—combination may result in myelosuppression.

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