Property:Explanation
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''Proteus mirabilis'' is the most common causative agent of struvite stones. It is an oxidase-negative, catalase-positive, urease-positive, gram-negative rod that has a characteristic “swarming” motility in cultures. ''Proteus mirabilis'' is a known pathogen of the urogenital tract. Other examples of urea-splitting organisms are ''Pseudomonas'', ''Klebsiella'', ''Staphylococcus'', and ''Mycoplasma''.<br/>
'''Educational Objective:''' ''Proteus mirabilis'' is a common causative agent of struvite stones. It is an oxidase-negative, catalase-positive, urease-positive, gram-negative rod with characteristic “swarming” motility in culture.<br/>
'''References:''' First Aid 2014 page 173 +
The patient has a high anion-gap metabolic acidosis. The approach to acid-base disturbances begins with assessment of blood pH. Since the patient's blood pH is 7.26, he is in a state of acidosis. Because acidosis can be metabolic or respiratory, bicarbonate concentration and pCO2 are helpful in distinguishing between the two. In this scenario, the patient has metabolic acidosis, manifesting with low bicarbonate levels. Had this patient had respiratory acidosis, his pCO2 would have been elevated, which is not the case. There are two types of metabolic acidosis: Normal anion gap (hyperchloremic) and high anion gap (normochloremic). To differentiate between them, the equation Anion Gap = Sodium - (Chloride + Bicarbonate) is used. A normal anion-gap ranges btween 8-12 mEq/L. Identification of the type of acid-base abnormality is crucial because it aids in the diagnosis. The patient in this scenario has a high anion gap metabolic acidosis. In this case, anion gap = 140 - (100 + 12) = 30 mEq/L. Among the list of options, only methanol intoxication manifests with a high anion gap metabolic acidosis. Other causes of high anion gap metabolic acidosis can be remembered with the mnemonic KARMEL: Ketoacidosis, Aspirin intoxication, Renal failure, Methanol, Ethanol, Lactic acidosis.<br/>
'''Educational Objective:''' Measurement of anion-gap in metabolic acidosis is essential to identify the likely diagnosis. Anion Gap = Sodium - (Chloride + Bicarbonate). A normal anion-gap ranges between 8-12 mEq/L. Common causes of high anion gap metabolic acidosis are KARMEL = Ketoacidosis - Aspirin toxicity – Renal failure – Methanol intoxication – Ethanol intoxication – Lactic acidosis<br/>
'''References:''' First Aid 2014 page 328 +
Pseudotumor cerebri (idiopathic intracranial hypertension) is a neurological condition characterized by elevated intracranial pressure (ICP). Common symptoms are headache, nausea, vomiting, and pulsatile tinnitus. The disease usually affects middle-aged obese women. Lumbar puncture and measurement of opening pressure is diagnostic and often therapeutic, either permanently or temporarily. Weight loss is key for management of pseudotumor cerebri. Patients are often prescribed furosemide, a loop diuretic, or acetazolamide, a diuretic that inhibits carbonic anhydrase in the proximal convoluted tubule. Acetazolamide is also indicated to relieve symptoms of altitude (not motion) sickness, glaucoma, and conditions that require alkalinization of urine. Furosemide is another pharmacologic option for pseudotumor cerebri.<br/>
'''Educational Objective:''' Pseudotumor cerebri is a neurological condition characterized by an elevated intracranial pressure. It generally affects middle-aged obese women. In addition to lumbar puncture and weight loss, acetazolamide can be used to treat pseudotumor cerebri. Other indications of acetazolamide include glaucoma, altitude sickness, and alkalinization of urine.<br/>
'''References:''' Wall M. Idiopathic intracranial hypertension. Neurologic clinics. 2010;28(3):593-617.<br>
First Aid 2014 page 547 +
The ureteric bud is derived from the caudal end of the mesonephros. It gives rise to the collecting ducts, the renal pelvicalyceal system, and the ureters. In contrast, the metanephros, which interacts with the ureteric bud, gives rise to renal structures, such as the glomerulus, proximal convoluted tubules, loop of Henle, and the distal convoluted tubules.<br/>
'''Educational Objective:''' The metanephros and ureteric bud interact to give rise to the renal and urinary structures. The metanephros gives rise to the glomerulus through the distal convoluted tubule, while the ureteric bud gives rise to the collecting duct, pelvicalyceal system, and the ureters.<br/>
'''References:''' First Aid 2014 page 522 +
Malignant hyperthermia is a condition characterized by a severe reaction to certain anesthetic drugs and muscle relaxants in patients with prior susceptibility to develop this condition. There are no clinical features specific for malignant hyperthermia. Typically, early signs include tachycardia and tachypnea, progressing to hyperthermia, generalized muscle rigidity, oliguria, arrhythmia and eventual death if treatment is not initiated. Recognition of early signs are important to warrant rapid intervention. Dantrolene is the medication of choice for the treatment of malignant hyperthermia. Dantrolene depresses excitation-contraction coupling in skeletal muscle by binding to the ryanodine receptor, and decreasing free intracellular calcium concentration.<br/>
'''Educational Objective:''' Dantrolene is the treatment of choice in malignant hyperthermia.<br/>
'''References:''' Hopkins PM. Malignant hyperthermia: advances in clinical management and diagnosis. Br J Anaesth. 2000;85(1):118-28.<br>
First Aid 2015 page 498 +
Curschmann's spirals are spiral shaped mucus plugs found in the sputum of patients who suffer from asthma or chronic bronchitis or those who have been chronic smokers. They are associated with excess sputum production and are composed mainly of glycoproteins. Although they have little diagnostic significance, they are a classic sign of obstructive lung diseases. In asthma, they are usually seen with Charcot-Leyden crystals.<br/>
'''Educational Objective:''' Curschmann's spirals are spiral shaped mucus plugs found in the sputum of patients who suffer from asthma or chronic bronchitis or in chronic smokers.<br/>
'''References:''' Antonakopoulos GN, Lambrinaki E, Kyrkou KA. Curschmann's spirals in sputum: Histochemical evidence of bronchial gland ductal origin. Diagn. Cytopathol. 1987;3(4):291-294. +
Identification is an immature psychological defense mechanism in which an individual subconsciously integrates characteristics of someone else into his/her own personality. Classically, patients model their behavior after someone they either admire or they perceive as more powerful. Similarly to other immature defense mechanisms, patients with features of identification have no insight and are not usually aware of this modeled behavior. This can sometimes complicate therapy, as it becomes difficult to separate the person's identity from the image they identify themselves with. Identification is also considered a subconscious attempt to boost one's self-esteem by taking on the characteristics of someone they consider is superior to them in depending on the social context. In this scenario the husband is exhibiting this form of immature defense. He models his abusive behavior after his father, and identifies himself as an abuser.<br/>
'''Educational Objective:''' Identification is an immature psychological defense mechanism in which an individual subconsciously integrates characteristics of someone else (usually a figure of authority) into his/her own personality.<br/>
'''References:''' Meissner WW. Notes of Identification: I. Origins in Freud. The Psychoanalytic Quarterly. 1970; 39(4):563-589. +
A minor is any individual under the age of 18 years. Generally, parental consent is required to treat minors. Parents may refuse the treatment of their minor children only when their refusal does not result in serious threat to the patient. If withholding treatment is dangerous to the patient and may result in adverse safety outcomes (e.g. life-threatening disease), the physician may initiate therapy on the basis of legal precedent. The physician may also treat minors without parental consent in the following cases:<br>
*Life-threatening conditions and parents cannot be contacted: Consent for treatment is implied
*Emancipated minors (marriage or army)
*Any of the following diagnoses: pregnancy, sexually transmitted infections, drugs abuse, or alcohol abuse<br><br/>
'''Educational Objective:''' A minor is any individual under the age of 18 years. Although parental consent is generally required to treat minors, minors presenting with STI and who do not wish to inform their parents may be treated without parental consent.<br/>
'''References:''' First Aid 2014 page 59 +
Myocardial infarction is one of the major causes of cardiac failure. Hypertension can also lead to heart failure by resulting in cardiac muscle abnormality such as left ventricular hypertrophy. Dyspnea on exertion is the most characteristic presentation in cases of heart failure. S3, rales, orthopnea, edema and jugular venous distension can also be seen in congestive cardiac failure. This patient’s presentation with dyspnea on exertion and the cardiac auscultation findings suggest heart failure. A low pitched sound after S2 can be an S3 gallop, which is characteristic of congestive heart failure. The patient’s history of hypertension and myocardial infarction are likely responsible for causing congestive heart failure.The best initial test to diagnose heart failure is a transthoracic echocardiogram.
'''Educational Objective:'''Transthoracic echocardiogram is the best initial test in evaluating heart failure.
'''References:''' Page 75,76,77,78 Master the boards step 2 CK second edition<br/>
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Metoprolol, sprinilactone , angiotensin converting enzyme inhibitors , angiotensin receptor blockers, implantable defibrillator and biventricular pace makers are associated with decreased mortality in heart failure patients. However, digoxin is only used to control symptoms of heart failure but has no mortality benefit.
'''Educational Objective:'''Digoxin and diuretics are used in heart failure just to control symptoms, but do not confer a mortality benefit.
'''References:''' Page 79,80,81 Master the boards Step 2 CK second edition<br/>
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The best initial therapy for heart failure is a loop diuretic to decrease preload. Reduced preload will relieve this patient’s acute symptoms .
'''Educational Objective:'''The standard of care for the acute treatment of heart failure includes a loop diuretic such as furosemide, along with oxygen, morphine and nitrates.
'''References:'''Page 83,84 Master the boards Step 2 CK second edition<br/>
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When arrhythmia is the cause of heart failure, the best next step in management is rapid synchronized cardioversion. Successful cardioversion causes the atrium and ventricles to contract coordinated in normal rhythm such that cardiac output can be maintained.
''' Educational Objective:''' Rapid synchronized cardioversion is the management of choice when arrhythmias like atrial fibrillation or ventricular tachycardia are the cause of pulmonary edema. To maintain cardiac output, heart chambers should be in regular rhythm.
'''References:''' References:: Page 82,83,84,85 Master the boards Step 2 CK second edition, page 55 Master the boards Step 3 2009 edition<br/>
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The above image demonstrates male breast enlargement known as gynecomastia. Gynecomastia is a side effect of spirinolactone due to its anti androgenic effect. Sprinolactone can be replaced with eplerenone , which is also a potassium sparing diuretic. Eplerenone also confers a mortality benefit in heart failure but does not cause gynecomastia.
'''Educational Objective:''' Gynecomastia is a side effect of spirinolactone use. Eplerenone can be substituted for spironolactone in these cases, as it does not have anti- androgenic side effects.
'''References:''' Page 79, 80 Master the boards Step 2 CK second edition<br/>
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There are two main epicardial arteries that supply the myocardium: the left coronary artery (LCA) and the right coronary artery (RCA). The heart is supplied by these two arteries and their branches in such a way that the LCA supplies mainly the left ventricle, whereas the RCA supplies the right atrium and ventricle, the SA node, the inferior wall, posterior interventricular septum, and posteromedial papillary muscle in approximately 85 % of the cases.
The RCA originates above the right cusp of the aortic valve. It travels down the right atrioventricular groove, towards the crux of the heart. In addition to supplying blood to the right ventricle (RV), the RCA supplies 25% to 35% of the left ventricle (LV). The LCA normally arises from the aortic sinus above the left cusp of the aortic valve and supplies the majority of the blood flow to the left ventricle. In fact, the LCA supplies the posterolateral side of the LV as well as the anterior part of the LV, which includes the anterolateral myocardium, the apex, the anterior interventricular septum, and the anterolateral papillary muscle.
The origin of the LCA is called the left main coronary artery, and it bifurcates into the following two main branches: Left anterior descending (LAD) artery and Left circumflex artery (LCx). The dominance of coronary circulation is determined by the type of arteries that supply the posterior and inferior wall of the left ventricle. The artery that supplies the posterior descending artery (PDA) and the posterolateral artery (PLA) determines the coronary dominance. Approximately 60 - 70% of the general population are right-dominant, 25% are co-dominant, and 15% are left-dominant.<br/>
'''Educational Objective:''' The heart is supplied by these two arteries and their branches in such a way that the LCA supplies mainly the left ventricle, whereas the RCA supplies the right atria and ventricle, the SA node, the inferior wall, posterior interventricular septum, and posteromedial papillary muscle in 85 % of the cases.<br/>
'''References:''' First Aid 2014 page 266
More than 80% of myocardial infarctions (MI) are caused by thrombus formation in the coronary arteries. Thrombosis causes ischemia to myocytes with insufficient myocardial perfusion within seconds. The acute phase following an MI is a critical period marked by high rates of cardiovascular complications and mortality. The risk of arrhythmia significantly increases following MI. Fatal ventricular arrythmias are considered the most common cause of post-MI mortality and the leading cause of death prior to hospitalization. Arrhythmias are thought to be caused by either the increased automaticity due to shortening of the action potential and refractory period in the membranes of ischemic cells or reperfusion injury caused by free oxygen species. The location of an MI is associated with the risk of arrhythmia. While anterior MI is associated with atrial fibrillation, atrial flutter, paroxysmal atrial tachycardia, and accelerated AV junctional rhythm (Anterior MI is associated with a sympathetic surge), posterior and inferior MI is associated with bradycardia and junctional escape rhythms (Posterior MI is associated with excessive vagal response because RCA usually supplies the posterior portion of the heart and the SA node). Although acute arrhythmias are significant complications post-MI, several other electrical and mechanical complications may also occur in the non-acute MI phase. Common complications post-MI include:
* Heart failure
* Cardiogenic shock
* Ventricular free wall rupture that may lead to cardiac tamponade
* Interventricular septum rupture that may cause septal defects (eg. VSD)
* Papillary muscle rupture and mitral regurgitation
* Ventricular pseudoaneurysm and aneurysm formation
* Fibrinous pericarditis
* Dressler syndrome<br/>
'''Educational Objective:''' The risk of arrhythmia significantly increases following MI. Fatal ventricular arrythmias are considered the most common cause of post-MI mortality and the leading cause of death prior to hospitalization.<br/>
'''References:''' O'Donnell L. Complications of MI: beyond the acute stage. Am J Nurs. 1996;96(9):25-30.<br>
First Aid 2014 page 290
Infection of an implanted foreign prosthetic material is a relatively common complication that is often caused by ''Staphylococcus epidermidis'' infection. ''S. epidermidis'' is a gram-positive coagulase-negative non-motile organism that causes biofilms that grow on surgical implants or catheters. ''S. epidermidis'' is a catalase-positive, coagulase-negative, facultative anaerobe. It has a weak positive reaction to nitrate reduction test. Also, ''S. epidermidis'' is sensitive to novobiocin. To distinguish ''S. epidermidis'' from other staphylococcal organisms, ''S. aureus'' is coagulase-positive and ''S. saprophyticus'' is novobiocin-resistant. An important virulence factor of ''S. epidermidis'' is its surface proteins that can result in the formation of antibiotic-resistant biofilms on plastic devices. Administration of antibiotics and surgical removal of the implanted device are generally both required for appropriate treatment of prosthetic material infection. Of note, ''S. epidermidis'' is part of the normal skin and mucosal microflora and often contaminates blood or urine cultures.<br/>
'''Educational Objective:''' ''S. epidermidis'' is a gram-positive, catalase-positive, coagulase-negative non-motile organism that is commonly associated with infections following prosthetic implant due to its ability to form antibiotic-resistant biofilms.<br/>
'''References:''' First Aid 2014 page 130 +
Paget's disease of the bone (osteitis deformans) is characterized by abnormal bone architecture due to increased bone cellular activity. It is caused by an increase in osteoclastic activity, which is presumed to be induced by an infectious process. Consequently, osteoblastic activity also increases. Nonetheless, a net increase in osteoclastic activity is still predominant, and a mosaic pattern of woven and lamellar bone with chalk-stick fractures is observed.
Paget's disease of the bone preferentially affects the axial skeleton (pelvis, femus, lumbar spine, skull, and tibia). The disease usually affects patients older than 55 years of age of European descent. The diagnosis of Paget's disease of the bone is usually incidental, and the majority of patients are asymptomatic and require no pharmacologic therapy. The most common symptom is bone pain, which may be a result of a combination of diseases that affect the elderly, such as coexisting Paget's disease of the bone and osteoarthritis. Few patients complain of deafness, which is usually caused by involvement of the skull. Physical examination is usually unremarkable, but bone deformity may be visible. Typically, work-up of patients demonstrates elevated serum alkaline phosphatase.
Paget's disease is associated with increased risk of arteriovenous shunts that cause high-output heart failure. Paget's disease is also associated with osteogenic sarcoma (osteosarcoma), a bone tumor that usually affects the metaphysis of long bones, obstructive hydrocephalus, and hypercalcemia due to prolonged immobilization. Treatment is generally reserved for symptomatic patients, where bisphosphonates are the optimal pharmacologic therapy for Paget's disease of the bone.<br/>
'''Educational Objective:''' Paget's disease is caused by a simultaneous increase in osteoclastic and osteoblastic activities that result in bone remodeling and a mosaic bone pattern. Paget's disease of the bone is associated with increased risk of high output heart failure due to arteriovenous shunts.<br/>
'''References:''' Ralston SH. Paget's disease of bone. N Engl J Med. 2013;368:644-50.<br>
First Aid 2014 page 420
Carpal tunnel syndrome (CTS) is the most common entrapment mononeuropathy. It is characterized by sensation of pain and paresthesias in the distribution of the median nerve (C5-T1) of the affected hand. The median nerve lies deep within the flexor retinaculum between the flexor digitorum profundus and the flexor digitorum superficialis and provides sensory innervation to the thumb and the index finger, middle finger, and lateral half of the ring finger on the dorsum of the hand. Patients with CTS often report pain that is worsened at night with loss of sleep. CTS should be suspected among both male and female patients of any age. The most important risk factors for the development of CTS include occupational activities, such as bending of the wrists (such as working at a keyboard). Other risk factors include dislocation of the lunate bone, which causes acute CTS, and chronic dialysis, which results in CTS due to β2-microglobulin amyloidosis. On physical examination, patients may have decreased sensation and reduced strength in the regions innervated by the median nerve. More advanced cases may demonstrate loss of the thenar eminence suggestive of muscle atrophy. Phalen's (maximal wrist extension) and Tinel's tests (light tapping on the wrist) are two provocative tests that may be helpful in the diagnosis of CTS. However, they are both signs of low sensitivity and specificity; and the diagnosis of CTS should always be confirmed by electrodiagnostic studies. Electrophysiologic findings include prolonged distal latency and delayed conduction velocity of the sensory and/or motor components of the median nerve. Although patients often complain of unilateral wrist pain, electrodiagnostic studies in CTS often reveal entrapment in both wrists with varying degrees of severity.<br/>
'''Educational Objective:''' Carpal tunnel syndrome (CTS) is a clinical syndrome caused by the entrapment of the median nerve at the level of the flexor retinaculum. Manifestations of CTS include sensations of pain and paresthesias in the distribution of the median nerve of the affected hand, which include the thumb and the index finger, middle finger, and lateral half of the ring finger on the dorsum of the hand. Diagnosis should always be confirmed by electodiagnostic studies, but Phalen's (maximal wrist extension) and Tinel's tests (light tapping on the wrist) are signs on physical examination that may suggest the diagnosis.<br/>
'''References:''' Solomon DH, Katz JN, Bohn R, et al. Nonoccupational risk factors for carpal tunnel syndrome. J Gen Intern Med. 1999;14(5):310-4.<br>
First Aid 2014 page 412, 414
Amiodarone is a class III antiarrhythmic drug that has effects of class Ia, II, III, and IV antiarrhythmics. Electrophysiological effects of amiodarone include prolongation of phase 3 of the action potential (repolarization) leading to an increase in AP duration, and increase of the refractory period causing a decrease in the heart rate. Amiodarone also increases the QT interval, however, it is not associated with an increase risk of torsade de pointes. Amiodarone has a chemical structure that closely resembles thyroxine, which replaces thyroxine at its receptor. The molecule also inhibits the action of type 1 5'-deiodinase that is responsible for the peripheral conversion of T4 to T3. Several other pathological effects on the thyroid gland and its hormones have been described including cytotoxic effects, and inhibition of feedback regulation. Clinically, these effects may manifest as either hypo- or hyperthyroidism, which is the main reason for the close follow-up of thyroid function among patients receiving amiodarone. Amiodarone also has several other side-effects including interstitial fibrosis, corneal deposits, peripheral neuropathy, and skin discoloration. The bluish skin discoloration (ceruloderma) associated with skin deposits of amiodarone is also known as "blue-man syndrome". It most commonly involves the face and is also associated with severe corneal deposits. It resolves within weeks to months of amiodarone discontinuation.<br/>
'''Educational Objective:''' Amiodarone is a class III antiarrhythmic associated with hypo or hyperthyroidism and bluish-grey discoloration with prolonged use.<br/>
'''References:''' Zimetbaum P. Amiodarone for atrial fibrillation. N Engl J Med. 2007;356(9):935-41.<br>
Enseleit F, Wyss CA, Duru F, Noll G, Ruschitzka F. Images in cardiovascular medicine. The blue man: amiodarone-induced skin discoloration. Circulation. 2006;113(5):e63.<br>
First Aid 2013 page 303 +
The patient in this scenario is presenting for recurrent hypoglycemic episodes that are most likely related to exogenous administration of insulin. The classical triad in of patients with true hypoglycemia is known as the Whipple's triad. It consists of (1) symptoms known or likely to be caused by hypoglycemia, (2) a low plasma glucose measured at the time of the symptoms, and (3) a relief of symptoms when glucose level is restored to normal. In patients who are not diabetic, a thorough work-up to uncover the etiology of hypoglycemia is indicated. Insulin levels followed by C-peptide (with or without proinsulin) measurement in patients with elevated insulin levels are required as a primary assessment. In patients with elevated C-peptide, further evaluation for sulfonylurea abuse, insulinoma, or autoimmune hypoglycemia. Autoimmune syndromes are a rare cause of hypoglycemia and can be diagnosed by screening for specific antibodies. Sulfonylureas are insulin secretagogues that increase endogenous insulin thus increasing C-peptide concentrations. In patients with low C-peptide i.e. low endogenous production of insulin, and high insulin levels, the cause is exogenous insulin administration and is almost always factitious. This patient is a victim of Munchausen's syndrome by proxy, where the mother induced a health condition in the child while under her care by injecting him with her own insulin.<br/>
'''Educational Objective:''' Exogenous insulin abuse is a common phenomenon that presents with true hypoglycemia (Whipple's triad) with elevated insulin levels and low C-peptide and proinsulin.<br/>
'''References:''' Scarlett JA, Mako ME, Rubenstein AH, et al. Factitious hypoglycemia. Diagnosis by measurement of serum C-peptide immunoreactivity and insulin-binding antibodies. N Engl J Med. 1977;297(19):1029-32. +