iatroX Rounds #49
The clues
- 1
A 66-year-old heavy smoker presents with a six-month history of progressive weakness in his thighs and difficulty rising from a low chair.
- 2
The patient describes that his strength paradoxically seems to improve for a short time after he starts walking or performing an activity.
- 3
He mentions a persistent dry mouth, and his wife notes he has been troubled by constipation and erectile dysfunction recently.
- 4
Neurological examination reveals proximal muscle weakness and absent knee jerks, but these reflexes are briefly elicitable immediately after the patient contracts his quadriceps for ten seconds.
- 5
Repetitive nerve stimulation at high frequencies, or following brief exercise, shows a marked increase in the amplitude of the compound muscle action potential.
- 6
Blood tests confirm the presence of serum antibodies directed against P/Q-type voltage-gated calcium channels.
Lambert-Eaton myasthenic syndrome is a rare autoimmune disorder of the neuromuscular junction where antibodies attack presynaptic voltage-gated calcium channels. It is frequently associated with an underlying malignancy, most commonly small cell lung cancer.
- Proximal limb weakness that improves with repeated contraction
- Autonomic involvement including dry mouth and impotence
- Post-tetanic potentiation of depressed or absent tendon reflexes
- Association with small cell lung cancer in over 50 percent of cases
for education and entertainment. not medical advice.