Question

PATIENT’S CHIEF COMPLAINTS

double vision
axial limb weakness
difficulty swallowing

PAST MEDICAL HISTORY

35 year old white female
fracture of radius at age 10

FAMILY MEDICAL HISTORY

mother diagnosed with mild osteoporosis
sister, age 29, has Type I diabetes
one daughter and two sons exhibiting no major health problems

PHYSICAL EXAMINATION

Height = 5’2”                                      
Weight = 115 lbs
Body temperature = 98.9^o F
Heart rate = 76 bpm
Blood pressure = 115/75 mm Hg
Respiratory Rate = 14 bpm

LABORATORY TESTS

Complete blood count (CBC) - normal
Standard laboratory tests - normal
EKG - normal
Chest X-ray – enlargement of upper mediastinum
Chest computed tomography (CAT scan) – smooth mass in upper mediastinum
Acetylcholine receptor antibodies elevated

6.  After evaluating the physical examination data and the laboratory tests, has your
     differential diagnosis changed?  If so, why?  Explain, specifically, what information
     contained in those two sections caused you to add or subtract a disorder from your
     differential diagnosis.

7.  What additional tests would you perform to confirm your diagnosis?

Answer 1

ANSWER

The most important findings  available from laboratory tests and CT scan are-

Chest CAT scan  – smooth mass in upper mediastinum
Acetylcholine receptor antibodies elevated

These two findings along with chief complaints of double vision, difficult swallowing and limb weakness points towards the diagnosis of MYASTHENIA GRAVIS.

REASON FOR MASS IN CHEST CT

The thymus gland , which stimulates the  immune system , is situated in the upper mediastinum .

The thymus gland triggers production of anti acetylcholine receptor antibodies

Due to this overactivity the thymus gland is abnormally large in these patients.

Sometimes, patients of Myasthenia might develop tumors of the thymus gland (thymomas).

Thus enlargement of thymus gland presents as a mass in mediastinum in Chest CT

NOTE- Thymus gland is larger in children and regresses in size with increasing age

Acetylcholine receptor antibodies

Postsynaptic Acetylcholine receptor antibodies are the main pathogenic agent in myasthenia gravis.. These antibodies reduce the number of Acetylcholine receptors.

CONFIRMATORY TESTS FOR MYASTHENIA GRAVIS

• Edrophonium Test: A short-acting drug called edrophonium chloride is given intravenously. If weakness, ( especially in the eye muscles) improves briefly and temporarily its Myasthenia gravis.
• Nerve conduction studies - A small electrical impulse is applied to a nerve resulting in muscle contraction. Muscles of Myasthenic patients shiws early signs of fatigue.
• Single fiber electromyography (EMG)- It may show abnormal neuromuscular transmission

  POINTS  TO PONDER
MYASTHENIA GRAVIS is an autoimmune neuromuscular disorder characterised by skeletal muscle weakness.

The most commonly affected muscles are those of the eyes, face, and swallowing, with chief complaints of double vision, ptosis, difficulty in swallowing and talking and limb weakness.

The onset of disease is usually sudden.

Incidence is more in females less then 40yrs

Those affected often have a large thymus or develop a thymoma.

LAMBERT-EATON MYASTHENIC SYNDROME

It is slso a autoimmune disorder affecting neuromuscular junction.

Patient may present with weakness of limbs

But the pathophysiology is that the  immune system attacks the calcium channels on presynaptic nerve endings that are required to trigger the release of acetylcholine.