A 68-year-old man with chronic obstructive pulmonary disease (COPD) experiences progressive dyspnea, wheezing, and cough over several days despite using inhaled glucocorticoids and bronchodilators. His shortness of breath rapidly worsens and emergency medical services (EMS) is called. The patient becomes unresponsive prior to EMS arrival and is found to have pulseless electrical activity. Cardiopulmonary resuscitation is begun, and he is endotracheally intubated. The patient regains spontaneous circulation on arrival to the emergency department and is found to have a large pneumothorax and exacerbation of COPD. His other medical conditions include hypertension, type 2 diabetes mellitus, and Parkinson disease. A chest tube is inserted, and the patient is admitted to the intensive care unit for further management. Over the next several days, his respiratory status gradually improves, but he remains unresponsive despite not receiving any sedation. The patient is also observed to have recurrent episodes of brief contractions of various muscle groups. Deep tendon reflexes are normal. Serum electrolytes are within normal limits. Which of the following is the most likely cause of the observed findings in this patient?

Question

A 68-year-old man with chronic obstructive pulmonary disease (COPD) experiences progressive dyspnea, wheezing, and cough over several days despite using inhaled glucocorticoids and bronchodilators.  His shortness of breath rapidly worsens and emergency medical services (EMS) is called.  The patient becomes unresponsive prior to EMS arrival and is found to have pulseless electrical activity.  Cardiopulmonary resuscitation is begun, and he is endotracheally intubated.  The patient regains spontaneous circulation on arrival to the emergency department and is found to have a large pneumothorax and exacerbation of COPD.  His other medical conditions include hypertension, type 2 diabetes mellitus, and Parkinson disease.  A chest tube is inserted, and the patient is admitted to the intensive care unit for further management.  Over the next several days, his respiratory status gradually improves, but he remains unresponsive despite not receiving any sedation.  The patient is also observed to have recurrent episodes of brief contractions of various muscle groups.  Deep tendon reflexes are normal.  Serum electrolytes are within normal limits.  Which of the following is the most likely cause of the observed findings in this patient?

Quizplus · Accepted Answer

Explanation: Myoclonus is characterized by sudden, involuntary muscle contraction or relaxation that results in movement of limbs or joints. It can occur due to genetic disorders, seizures, medications, or prolonged hypoxia. This patient likely has posthypoxic myoclonus (PHM), a form of secondary myoclonus that commonly occurs after cardiac arrest. PHM can be subdivided into acute and chronic forms: Myoclonus status epilepticus (MSE) is the acute form of PHM that typically develops within 24 hours after the initial hypoxic insult while the patient is still unconscious. It is characterized by a generalized (often symmetric) myoclonus that typically involves the axial, limb, and facial muscles; intermittent eye opening, upward gaze deviation, and swallowing movements are also common. Persistent MSE is considered a marker of poor prognosis. Lance-Adams syndrome, the chronic form of PHM, presents days to weeks after the initial insult once the patient has regained consciousness. It is typically focal in nature and exacerbated by action; negative (relaxation) myoclonus also occurs, leading patients to drop objects or fall. An electroencephalogram should be obtained to help distinguish between other forms of seizure and PHM. The management of both the acute and chronic forms of PHM involves administration of antiepileptic agents (eg, clonazepam, levetiracetam) and supportive care. (Choice A) Critical illness polyneuropathy commonly occurs after a prolonged stay in the intensive care unit but is characterized by peripheral weakness and reduced reflexes. (Choice B) Medications such as statins and colchicine can be myotoxic and result in rhabdomyolysis. In addition, prolonged immobility due to the therapeutic use of paralytic agents can lead to compression of muscles, causing ischemia and necrosis. However, symptoms include muscle tenderness and weakness, not myoclonus. (Choice C) Antipsychotic (eg, haloperidol) or antiemetic medications (eg, metoclopramide) can cause extrapyramidal side effects, resulting in involuntary muscle group contraction (ie, dystonia) or motor restlessness (akathisia). However, akathisia would only occur in awake patients, and dystonias typically result in sustained contractions that are usually quite distinguishable from myoclonus (eg, torticollis, chorea). (Choice D) Muscle denervation can occur in neurodegenerative diseases such as amyotrophic lateral sclerosis, postpolio syndrome, and spinobulbar muscular atrophy, resulting in fasciculations rather than myoclonus. Fasciculations usually result only in visible twitching of muscles without movement of joints. Educational objective: Myoclonus is characterized by sudden, involuntary muscle contraction or relaxation that results in movement of limbs or joints. Posthypoxic myoclonus is often seen after cardiac arrest; the acute form (myoclonus status epilepticus [MSE]) occurs while patients are still unconscious and is characterized by generalized (often symmetric) myoclonus that involves the axial, limb, and facial muscles. Prolonged MSE is a marker of poor prognosis. References: Post-hypoxic myoclonus: current concepts, neurophysiology, and treatment. (http://www.ncbi.nlm.nih.gov/pubmed/27708982) Post-hypoxic myoclonus: differentiating benign and malignant etiologies in diagnosis and prognosis. (http://www.ncbi.nlm.nih.gov/pubmed/30214979)

A 68-Year-Old Man with Chronic Obstructive Pulmonary Disease (COPD) Experiences