A 59-year-old man comes to the office due to progressive weakness for the past several weeks. The patient has had difficulty getting out of bed and climbing stairs in the morning, which improves gradually as he "warms up the muscles" with continued use. He has also had to drink water more frequently due to dry mouth and has had episodic double vision. The patient also reports difficulty achieving erections despite having a good libido. Neurologic examination shows decreased strength of the hip flexors and diminished knee reflexes. Repeat examination after lower extremity isometric exercise shows normalization of the muscle strength and deep tendon reflexes. Which of the following conditions is most closely associated with this patient's current disease process?

Question

A 59-year-old man comes to the office due to progressive weakness for the past several weeks.  The patient has had difficulty getting out of bed and climbing stairs in the morning, which improves gradually as he "warms up the muscles" with continued use.  He has also had to drink water more frequently due to dry mouth and has had episodic double vision.  The patient also reports difficulty achieving erections despite having a good libido.  Neurologic examination shows decreased strength of the hip flexors and diminished knee reflexes.  Repeat examination after lower extremity isometric exercise shows normalization of the muscle strength and deep tendon reflexes.  Which of the following conditions is most closely associated with this patient's current disease process?

Quizplus · Accepted Answer

11ec160b_3a57_d9ea_9249_dd13845b161e_MD0001_00 This patient with proximal muscle weakness and decreased deep tendon reflexes that improve with exercise has Lambert-Eaton myasthenic syndrome (LEMS). LEMS is an immune-mediated disorder of the neuromuscular junction characterized by autoantibodies directed at the presynaptic voltage-gated calcium channel, resulting in decreased acetylcholine release and muscle weakness. LEMS is strongly associated with small cell lung cancer, likely due to the immune recognition of voltage-gated calcium channels that are present on the malignant cells. Patients typically develop progressive proximal muscle weakness that manifests in the form of gait alteration and difficulty arising from a chair or climbing stairs. Autonomic symptoms, such as dry mouth or impotence, are common. Cranial nerve (particularly ptosis) and respiratory muscle involvement may occur but typically manifest later in the disease course. Patients may experience postexercise facilitation, in which muscle strength and deep tendon reflexes improve with exercise or repetitive movements (due to accumulation of calcium within the axon terminal). This effect is also seen in repetitive nerve stimulation studies. (Choice A) Guillain-Barré syndrome is an acute postinfectious polyneuropathy often associated with Campylobacter jejuni infections. It is characterized by rapidly progressive, ascending paralysis that does not improve with repetitive movement. (Choice B) Paraneoplastic syndromes associated with gastric adenocarcinoma include abrupt onset of numerous seborrheic keratoses (Leser-Trélat sign) and acanthosis nigricans. (Choice C) Giant cell arteritis is characterized by headache, visual changes, and jaw claudication in older adults. It is not associated with LEMS. (Choice D) Medullary thyroid cancer may be associated with multiple endocrine neoplasia (MEN) type 2 (both A and B variants). MEN 2A is associated with pheochromocytoma and hyperparathyroidism, whereas MEN 2B is associated with pheochromocytoma and mucosal neuromas. (Choice F) Thymic neoplasia or thymomas are commonly associated with myasthenia gravis (MG), another autoimmune neuromuscular condition. MG is often confused with LEMS; however, in MG facial, periocular, and bulbar weakness typically presents before extremity weakness. In addition, the weakness worsens with exercise, deep tendon reflexes typically remain intact, and autonomic dysfunction is rare. Educational objective: Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular disorder characterized by autoantibodies against presynaptic voltage-gated calcium channels. It causes progressive proximal muscle weakness and decreased deep tendon reflexes that improve with exercise (postexercise facilitation); cranial nerve involvement and autonomic symptoms may also occur. LEMS is strongly associated with small cell lung cancer.

A 59-Year-Old Man Comes to the Office Due to Progressive