A 44-year-old woman comes to the office with muscle weakness over the past several months. She has difficulty combing her hair and, occasionally, difficulty holding up her head, particularly after prolonged sitting or standing. The patient has had no difficulty walking or getting up from a chair. She has also had 2 episodes of double vision while driving home from work. The patient takes rosuvastatin for hyperlipidemia and lisinopril for hypertension. Blood pressure is 142/84 mm Hg and pulse is 76/min. Neurologic examination shows mild right ptosis, symmetric proximal muscle weakness in the upper extremities, and weakness in the head extensors. Muscle bulk and tone are normal and there is no muscle tenderness. Which of the following is the most likely site of the pathology in this patient?

Question

A 44-year-old woman comes to the office with muscle weakness over the past several months.  She has difficulty combing her hair and, occasionally, difficulty holding up her head, particularly after prolonged sitting or standing.  The patient has had no difficulty walking or getting up from a chair.  She has also had 2 episodes of double vision while driving home from work.  The patient takes rosuvastatin for hyperlipidemia and lisinopril for hypertension.  Blood pressure is 142/84 mm Hg and pulse is 76/min.  Neurologic examination shows mild right ptosis, symmetric proximal muscle weakness in the upper extremities, and weakness in the head extensors.  Muscle bulk and tone are normal and there is no muscle tenderness.  Which of the following is the most likely site of the pathology in this patient?

Quizplus · Accepted Answer

11ec25c8_d488_e14c_bc81_0fd6ba566cc5_MD0003_00 Depending on the distribution of clinical findings, muscle weakness can be caused by disorders of the upper motor neuron, lower motor neuron, peripheral nerve, neuromuscular junction (NMJ), or muscle fibers. This patient with ptosis and fatigable proximal muscle weakness that worsen with prolonged use (eg, after work, while holding up the head when sitting/standing, while brushing hair) likely has myasthenia gravis. Myasthenia gravis is a NMJ disorder caused by autoantibodies against acetylcholine receptors in the motor end plate. Patients typically have fluctuating and fatigable extraocular (eg, diplopia, ptosis) and bulbar (eg, dysarthria, dysphagia) muscle weakness. They may also experience symmetric proximal weakness involving the neck (eg, difficulty holding up the head) and upper extremities (eg, difficulty combing hair). Sensation, reflexes, muscle bulk/tone, and autonomic function are usually intact. (Choice A) Stroke is an example of a motor cortex (upper motor neuron) lesion that can cause acute contralateral flaccid paralysis followed by spastic paralysis and hyperreflexia. Patients typically do not have fatigable weakness or ptosis that improves with rest. (Choice C) Guillain-Barré syndrome is caused by inflammatory demyelination and/or motor axonal neuropathy, which leads to rapidly progressive symmetric ascending muscle paralysis. Symptoms are generally preceded by infection (eg, Campylobacter jejuni, viruses) and associated with reduced/absent reflexes and paresthesias. (Choice D) Amyotrophic lateral sclerosis is characterized by progressive motor neuron degeneration, resulting in upper (eg, spastic paralysis) and lower (eg, muscle atrophy, fasciculations) motor neuron signs. Patients typically have asymmetric limb and bulbar muscle weakness and fasciculations. (Choice E) Statin-induced myopathy and polymyositis are caused by inflammation of the muscle fascicles. Patients often present with proximal muscle weakness (eg, difficulty getting up from a chair) and mild tenderness affecting both the upper and lower extremities. Ocular and bulbar weakness is not characteristic. (Choice F) Lesions of the subcortical nuclei (eg, basal ganglia) typically result in extrapyramidal signs (eg, rigidity, bradykinesia, tremor, chorea) such as those seen in Parkinson or Huntington disease. (Choice G) Multiple sclerosis is characterized by autoimmune demyelination of the white matter tracts in the central nervous system. It typically affects women age <50 and presents with neurologic deficits disseminated in space and time (eg, optic neuritis, internuclear ophthalmoplegia, myelitis), not fatigable weakness of the proximal and extraocular muscles, as described in this patient. Educational objective: Neuromuscular junction disorders are generally characterized by muscle weakness in the absence of upper or lower motor neuron signs. Myasthenia gravis is a neuromuscular disease that typically presents with fluctuating and fatigable extraocular (eg, diplopia, ptosis) and bulbar (eg, dysarthria, dysphagia) muscle weakness as well as symmetrical proximal weakness of the neck and extremities (upper more than lower). References: Neuromuscular junction disorders. (http://www.ncbi.nlm.nih.gov/pubmed/23524069)

A 44-Year-Old Woman Comes to the Office with Muscle Weakness