OCULAR MYASTHENIA GRAVIS : DIAGNOSTIC PEARLS

OCULAR MYASTHENIA GRAVIS: DIAGNOSTIC PEARLS

CLINICAL TESTS

• SLEEP TEST :  Improvement in muscle activity after 30 minutes of rest with closed eyes.
• ICE PACK TEST : Improvement in ptosis (after 2 minutes) and extraocular muscle activity (after 5 minutes) after placing ice pack over closed eyelids. improvement of atleast 2 mm in ptosis is required to consider the test as positive.

PHARMACOLOGICAL TESTS 

•  EDROPHONIUM TEST :  DOSE - I.V edrophonium 0.10mg/kg in children and upto 10mg in adults.

           Initially 2mg of dose is given to look for any adverse effect, if not 3-4 mg is injected further                upto maximum dose of 10 mg. 

           Onset of action : within 60 seconds.

            Effect lasts for 5-10 minutes.

           Improvement in ptosis or muscle activity suggests positive test.

           Contraindicated in bronchial asthama and cardiac patients.

• NEOSTIGMINE TEST : DOSE - 1.5 mg in adults, injected intramuscularly in deltoid region.

          Onset of action: 15-30 minutes. Effect lasts for several hours (longer duration of action).

          Contraindications : Same as Edrophonium.

LABORATORY INVESTIGATIONS

• Positive anticholine-esterase receptor antibody (AChR-Ab) titres confirm the diagnosis.
• Repeatative nerve fiber stimulation & single fiber electromyography.

IMAGING may reveal thymic hyperplasia (70%) or thymoma (10-15%) in some cases.

4-5% patients may have concurrent autoimmune thyroid disease.