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{{WBRQuestion | {{WBRQuestion | ||
|QuestionAuthor={{Ochuko}} | |QuestionAuthor={{Ochuko}} (Reviewed by {{YD}}) | ||
|ExamType=USMLE Step 1 | |ExamType=USMLE Step 1 | ||
|MainCategory=Microbiology | |MainCategory=Microbiology | ||
| Line 21: | Line 21: | ||
|MainCategory=Microbiology | |MainCategory=Microbiology | ||
|SubCategory=Pulmonology, Infectious Disease | |SubCategory=Pulmonology, Infectious Disease | ||
|Prompt=A 46- year old | |Prompt=A 46-year-old homeless man presents to the emergency department (ED) with complaints of fever, dyspnea, and non-productive cough. He explains that his symptoms did not occur acutely, but have progressively worsened over the past few weeks. The patient does not smoke, but drinks 6-8 beers every day. He lives in a shelter for the homeless. His past medical history is significant for end-stage renal disease and kidney transplantation, for which he currently receives immunosuppressive therapy. In the ED, the patient's temperature is 39.7 °C (103.5 °F), blood pressure is 138/86 mmHg, and heart rate is 102/min. He appears very thin and severely malnourished. Physical examination is remarkable for coarse crackles during anterior auscultation of the right upper lung field. Chest x-ray demonstrates nodular infiltrates and cavitations in the upper right lobe. The patient is admitted and is started on broad-spectrum antimicrobial therapy. The next day, sputum culture shows an aerobic, gram-positive rod with a beaded acid-fast appearance on microscopy. Which antimicrobial agent is the optimal monotherapeutic option to treat this patient's condition? | ||
|Explanation= | |Explanation=Nocardiosis is an opportunistic infection that is caused by ''Nocardia asteroides'', an aerobic, weakly acid-fast, gram-positive rod with branching filaments. Although ''N. asteroides'' is also variably acid fast, it may be distinguished from ''Mycobacterium'' species by its "beaded" acid-fast appearance on microscopy. Although ''Actinomyces'' also appears as a gram-positive rod with branching filaments, it is anaerobic and is not acid-fast. It commonly affects immunocompromised patients, such as patients with malignancies, HIV-positive patients, and individuals on immunosuppressive therapy. ''N. asteroides'' is usually transmitted by inhalation. However, ''N. asteroides'' may colonize immunocompetent individuals and patients with structural lung disease (cystic fibrosis and bronchiectasis) without causing a pulmonary infection. Manifestations in the human host appear subacutely, similar to infections with ''Mycoplasma''; they include high-grade fever, non-productive cough, dyspnea, hemoptysis, and constitutional symptoms such as weight loss, fatigue, and night sweats. Chest x-ray typically demonstrates nodular or consolidation infiltrates along with cavitary lesions and/or parapneumonic pleural effusions. The organism spreads contiguously to the pericardium and mediastinum or hematogenously to the CNS (cerebral nocardiosis) and causes extrapulmonary manifestations, such as abscess formation and chronic granulomas. Sulfonamides, such as sulfadiazine and sulfisoxazole, are the first line antimicrobial agents to treat nocardiosis. Prior to confirmation with susceptibility, empirical combination therapy that includes sulfonamides (e.g. TMP-SMX and imipenem/ceftriaxone) has been frequently administered to patient with nocardiosis given the improved efficacy of the combination compared to monotherapy. | ||
|AnswerA= | |AnswerA=Sulfisoxazole | ||
|AnswerAExp= | |AnswerAExp=Sulfonamides, such as sulfadiazine and sulfisoxazole, are the first line antimicrobial agents to treat nocardiosis. | ||
|AnswerB= | |AnswerB=Trimethoprim | ||
|AnswerBExp= | |AnswerBExp=Trimethoprim alone is insufficient to treat nocardiosis. However, TMP-SMX, which includes sulfonamide, is a possible pharmacological therapy against ''Nocardia''. | ||
|AnswerC= | |AnswerC=Rifampin, isoniazid, ethambutol, and pyrazinamide | ||
|AnswerCExp= | |AnswerCExp=The combinatoin of rifampin, isoniazid, ethambutol, and pyrazinamide is administered to patients with active tuberculosis (TB). TB should always be in the differential diagnosis of nocardiosis, since it manifests similarly and has similar risk factors. However, this patient's sputum culture reveals aerobic, gram-positive rods. Unlike TB, the acid-fast appearance in ''Nocardia'' is often described as "beaded". | ||
|AnswerD= | |AnswerD=Penicillin | ||
|AnswerDExp= | |AnswerDExp=Penicillin is not an effective therapy to treat nocardiosis. In contrast, penicillin is the first line agent against ''Actinomyces'', which are anaerobic, gram-positive rods with branching filaments. ''Actinomyces'' should always be in the differential diagnosis of ''Nocardia''. Unlike ''Nocardia'', ''Actinomyces'' is anaerobic and is not acid-fast. | ||
|AnswerE= | |AnswerE=Rifabutin | ||
|AnswerEExp= | |AnswerEExp=Rifamycins (rifampin and rifabutin) are not effective to treat nocardiosis. Rifampin is among the combination therapy to treat tuberculosis. Rifabutin is a more expensive rifamycin that may also be used to treat tuberculosis, but it is usually reserved for prophylaxis against disseminated MAC among HIV-positive patients. | ||
|EducationalObjectives=Nocardia asteroides | |EducationalObjectives=Nocardiosis is an opportunistic infection that is caused by ''Nocardia asteroides'', an aerobic, weakly acid-fast, gram-positive rod with branching filaments. Sulfonamides, such as sulfadiazine and sulfisoxazole, are the first line antimicrobial agents to treat nocardiosis. | ||
|References=First Aid 2014 page 134 | |References=Wilson JW. Nocardiosis: updates and clinical overview. Mayo Clin Proc. 2012;87(4):403-7.<br> | ||
|RightAnswer= | First Aid 2014 page 134 | ||
|WBRKeyword= | |RightAnswer=A | ||
|WBRKeyword=Nocardia, Nocardiosis, Sulfonamides, Sulfisoxazole, Sulfadiazine, TMP-SMX, Fever, Chest pain, Dyspnea, Gram-positive, Antibiotics, Branching filaments, Rods, Acid-fast, | |||
|Approved=Yes | |Approved=Yes | ||
}} | }} | ||
Revision as of 16:17, 10 November 2014
| Author | [[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Yazan Daaboul, M.D.)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::Pulmonology, SubCategory::Infectious Disease |
| Prompt | [[Prompt::A 46-year-old homeless man presents to the emergency department (ED) with complaints of fever, dyspnea, and non-productive cough. He explains that his symptoms did not occur acutely, but have progressively worsened over the past few weeks. The patient does not smoke, but drinks 6-8 beers every day. He lives in a shelter for the homeless. His past medical history is significant for end-stage renal disease and kidney transplantation, for which he currently receives immunosuppressive therapy. In the ED, the patient's temperature is 39.7 °C (103.5 °F), blood pressure is 138/86 mmHg, and heart rate is 102/min. He appears very thin and severely malnourished. Physical examination is remarkable for coarse crackles during anterior auscultation of the right upper lung field. Chest x-ray demonstrates nodular infiltrates and cavitations in the upper right lobe. The patient is admitted and is started on broad-spectrum antimicrobial therapy. The next day, sputum culture shows an aerobic, gram-positive rod with a beaded acid-fast appearance on microscopy. Which antimicrobial agent is the optimal monotherapeutic option to treat this patient's condition?]] |
| Answer A | AnswerA::Sulfisoxazole |
| Answer A Explanation | AnswerAExp::Sulfonamides, such as sulfadiazine and sulfisoxazole, are the first line antimicrobial agents to treat nocardiosis. |
| Answer B | AnswerB::Trimethoprim |
| Answer B Explanation | AnswerBExp::Trimethoprim alone is insufficient to treat nocardiosis. However, TMP-SMX, which includes sulfonamide, is a possible pharmacological therapy against ''Nocardia''. |
| Answer C | AnswerC::Rifampin, isoniazid, ethambutol, and pyrazinamide |
| Answer C Explanation | [[AnswerCExp::The combinatoin of rifampin, isoniazid, ethambutol, and pyrazinamide is administered to patients with active tuberculosis (TB). TB should always be in the differential diagnosis of nocardiosis, since it manifests similarly and has similar risk factors. However, this patient's sputum culture reveals aerobic, gram-positive rods. Unlike TB, the acid-fast appearance in Nocardia is often described as "beaded".]] |
| Answer D | AnswerD::Penicillin |
| Answer D Explanation | [[AnswerDExp::Penicillin is not an effective therapy to treat nocardiosis. In contrast, penicillin is the first line agent against Actinomyces, which are anaerobic, gram-positive rods with branching filaments. Actinomyces should always be in the differential diagnosis of Nocardia. Unlike Nocardia, Actinomyces is anaerobic and is not acid-fast.]] |
| Answer E | AnswerE::Rifabutin |
| Answer E Explanation | [[AnswerEExp::Rifamycins (rifampin and rifabutin) are not effective to treat nocardiosis. Rifampin is among the combination therapy to treat tuberculosis. Rifabutin is a more expensive rifamycin that may also be used to treat tuberculosis, but it is usually reserved for prophylaxis against disseminated MAC among HIV-positive patients.]] |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::Nocardiosis is an opportunistic infection that is caused by Nocardia asteroides, an aerobic, weakly acid-fast, gram-positive rod with branching filaments. Although N. asteroides is also variably acid fast, it may be distinguished from Mycobacterium species by its "beaded" acid-fast appearance on microscopy. Although Actinomyces also appears as a gram-positive rod with branching filaments, it is anaerobic and is not acid-fast. It commonly affects immunocompromised patients, such as patients with malignancies, HIV-positive patients, and individuals on immunosuppressive therapy. N. asteroides is usually transmitted by inhalation. However, N. asteroides may colonize immunocompetent individuals and patients with structural lung disease (cystic fibrosis and bronchiectasis) without causing a pulmonary infection. Manifestations in the human host appear subacutely, similar to infections with Mycoplasma; they include high-grade fever, non-productive cough, dyspnea, hemoptysis, and constitutional symptoms such as weight loss, fatigue, and night sweats. Chest x-ray typically demonstrates nodular or consolidation infiltrates along with cavitary lesions and/or parapneumonic pleural effusions. The organism spreads contiguously to the pericardium and mediastinum or hematogenously to the CNS (cerebral nocardiosis) and causes extrapulmonary manifestations, such as abscess formation and chronic granulomas. Sulfonamides, such as sulfadiazine and sulfisoxazole, are the first line antimicrobial agents to treat nocardiosis. Prior to confirmation with susceptibility, empirical combination therapy that includes sulfonamides (e.g. TMP-SMX and imipenem/ceftriaxone) has been frequently administered to patient with nocardiosis given the improved efficacy of the combination compared to monotherapy. Educational Objective: Nocardiosis is an opportunistic infection that is caused by Nocardia asteroides, an aerobic, weakly acid-fast, gram-positive rod with branching filaments. Sulfonamides, such as sulfadiazine and sulfisoxazole, are the first line antimicrobial agents to treat nocardiosis. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Nocardia, WBRKeyword::Nocardiosis, WBRKeyword::Sulfonamides, WBRKeyword::Sulfisoxazole, WBRKeyword::Sulfadiazine, WBRKeyword::TMP-SMX, WBRKeyword::Fever, WBRKeyword::Chest pain, WBRKeyword::Dyspnea, WBRKeyword::Gram-positive, WBRKeyword::Antibiotics, WBRKeyword::Branching filaments, WBRKeyword::Rods, WBRKeyword::Acid-fast |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |