A 22-year-old primigravida at 34 weeks gestation is brought to the emergency department by ambulance due to sudden loss of consciousness followed by generalized shaking. The paramedics initiated an intravenous magnesium sulfate bolus, which was infusing rapidly when the patient arrived at the hospital. She says she is very tired and has blurry vision and a headache. The patient also has muscle pain and sore joints and is unable to move her right arm. Blood pressure is 145/98 mm Hg, pulse is 112/min, and respirations are 16/min. She holds the right arm adducted and internally rotated. Examination shows loss of external rotation of the right arm but no sensory deficits. Deep tendon reflexes are 2+ bilaterally, and handgrip and wrist strength are preserved on both sides. Urinalysis shows 3+ protein. Which of the following is the most likely cause of this patient's right arm findings?

A. Anterior shoulder dislocation
B. Magnesium toxicity
C. Posterior shoulder dislocation
D. Postictal (Todd) paralysis
E. Radial nerve compression

Correct Answer- C. Posterior Shoulder Dislocation

🧠 Why Posterior Shoulder Dislocation (In Short)

 Seizures cause forceful muscle contractions

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Posterior shoulder dislocation

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Shoulder dislocation is marked by the arm being held adducted and internally rotated

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🧠 Loss of external rotation of the arm is a key diagnostic finding in posterior shoulder dislocation

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 No sensory deficits → confirms no nerve injury

Detailed Answer

Pregnancy Complication: Preeclampsia

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Eclampsia (Seizure in preeclampsia)

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Eclampsia causes seizures (due to cerebral edema and vasospasm)

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Increased BP → ↑ vascular permeability → cerebral edema → risk of seizures

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Magnesium sulfate bolus (to prevent seizures in preeclampsia)

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Magnesium sulfate causes neuromuscular blockade

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Magnesium inhibits calcium influx → prevents acetylcholine release

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Decreased neuromuscular transmission

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Muscle weakness and generalized fatigue

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Blurry vision, headache (due to cerebral effects)

Seizure activity (generalized shaking)

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Seizure → violent muscle contractions and abnormal joint movements

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Shoulder joint forcefully displaced due to muscle contractions

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Shoulder Joint Dislocation Mechanism

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Seizures often cause violent muscle contractions

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Excessive force on the shoulder joint during a seizure

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Posterior shoulder dislocation occurs (less common than anterior dislocation)

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Posterior dislocation leads to arm being held adducted and internally rotated

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Loss of external rotation of the arm (key sign of posterior dislocation)

Explanation of Other Options

Anterior Shoulder Dislocation
- More common than posterior dislocation
- Presents with arm in externally rotated and abducted position
- Does not match the internally rotated arm seen in this case

Magnesium Toxicity
- Magnesium toxicity causes generalized muscle weakness, fatigue, reflexes ↓
- Does not specifically explain the arm position (adducted, internally rotated)
- Magnesium toxicity leads to neuromuscular blockade but does not lead to specific shoulder joint dislocation

Postictal (Todd) Paralysis
- Postictal paralysis causes transient weakness after a seizure
- Typically resolves in hours and does not cause abnormal shoulder positioning (adduction/ internal rotation)
- This patient still has persistent arm findings and no other postictal signs

Radial Nerve Compression
- Radial nerve compression usually causes wrist drop or difficulty with hand movement
- Does not explain the shoulder position and loss of external rotation
- No hand weakness or wrist dysfunction observed in this patient

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Your Brother in This Struggle,

Dr. Shoaib Ahmad