My patient with anemia has an abnormally high mean red blood cell corpuscular volume (MCV). What conditions should I routinely consider as a cause of his macrocytic anemia?

Anemia with mean corpuscular volume (MCV) above the upper limit of normal (usually ≥ 100 fL) is considered macrocytic anemia. The numerous causes of macrocytic anemia can be divided into major categories (1,2) (Figure 1).

First, a reticulocyte production index should be calculated and if elevated the MCV can be above the normal range due to the large size of reticulocytes. Once high MCV is not thought to be related to reticulocytosis, the majority of macrocytic anemias can be categorized according to one of two major mechanisms: 1. Liver disease; and  2. Impairment of DNA synthesis, which includes nutritional deficiencies (folate, B12), drug effect (e.g co-trimoxazole, anti-neoplastic agents and certain anti-retroviral drugs) and “idiopathic” causes (myelodysplastic syndromes).

Mild macrocytosis can also be seen in hypothyroidism and hypoproliferative anemias such as aplastic anemia.  Macrocytosis without anemia or liver disease can also be a manifestation of heavy alcohol intake.

Macrocytic anemia in liver disease is due to excess lipid deposition in the red blood cell (RBC) membrane, not impairment of DNA synthesis. Enlarged RBCs are usually round and  often have a targeted appearance in liver disease; acanthocytes (spur cells) may also be present (Fig 2). In contrast, in disorders of impaired DNA synthesis, enlarged RBCs are often oval-shaped (macro-ovalocytes) (Fig 3).

Other common abnormalities seen with macrocytic anemia include hypersegmented neutrophils (eg, induced by B12 or folate deficiency), and in the case of myelodysplastic syndromes, hypogranulated neutrophils and Pelger-Huet neutrophil abnormalities.

Bonus pearl: Did you know that the MCV unit, fL, stands for femtoliters or 1/1,000,000,000,000,000 L? 

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Figure 1. Major causes of macrocytic anemia. MDS: myelodysplastic syndrome.

 

Macrocytic_Anemia_Figure 1

Fig 2. Round macrocytes with targeting and abundant acanthocytes (spur cells) in a patient with hepatic cirrhosis.

 

Macrocytic_Anemia_Figure 2

Fig 3. Oval macrocytes in a patient with large granular cell leukemia and an MCV of 125 fL who received cyclophosphamide.

References

  1. Ward PC. Investigation of Macrocytic Anemia. Postgrad Med 1979; 65: 203-207. https://www.ncbi.nlm.nih.gov/pubmed/368738
  2. Green R, Dwyre DM. Evaluation of macrocytic anemias. Semin Hematol 2015; 52: 279-286. https://www.sciencedirect.com/science/article/abs/pii/S0037196315000554

 

Contributed by Tom Spitzer, MD, Director of Cellular Therapy and Transplantation Laboratory, Massachusetts General Hospital, Boston, MA.

My patient with anemia has an abnormally high mean red blood cell corpuscular volume (MCV). What conditions should I routinely consider as a cause of his macrocytic anemia?

When should I consider prophylaxis for Pneumocystis pneumonia (PCP) in my patient on prednisone?

It is generally recommended that patients on ≥20 mg of daily prednisone (or its equivalent) for ≥1 month be considered for PCP prophylaxis. 1

Couple of studies in 1990s helped define the dose and duration of corticosteroids (CS) that should prompt PCP prophylaxis. A Mayo Clinic study of patients without AIDS found that a median daily CS dose of 30 mg of prednisone or equivalent—with 25% of patients receiving as little as 16 mg of prednisone daily— was associated with PCP.The median duration of CS therapy before PCP was 12 weeks. A similar study found a mean CS dose of 33 mg of prednisone or equivalent with mean duration of 7 months (range 1-154 months) among patients with PCP without AIDS. 3

A 2018 retrospective study4  of patients with rheumatic diseases receiving prolonged high-dose CS therapy (≥30 mg prednisone for ≥4 weeks) found that PCP prophylaxis with trimethoprim/sulfamethoxazole (TMP/STX) resulted in 93% reduction in the incidence of PCP with an overall number needed to treat (NNT) of 52. It was suggested that PCP prophylaxis could be discontinued in patients receiving < 15 mg of prednisone daily.

Bonus Pearl: Did you know that TMP/STX may be given either as double-strength 3x/week or single-strength daily? 5,6

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References

1. Limper AH, Knox KS, Sarosi SA, et al. An official American Thoracic Society statement: Treatment of fungal infections in adult pulmonary and critical care patients. Am J Respir Crit Care Med 2011;183:96-128. https://www.ncbi.nlm.nih.gov/pubmed/21193785

2. Yale SH, Limper AH. Pneumocystis carinii pneumonia in patients without acquired immunodeficiency syndrome: associated illness and prior corticosteroid therapy. Mayo Clin Proc 1996;71:5-13. https://www.sciencedirect.com/science/article/abs/pii/S0025619611649148

3. Arend SM, Kroon FP, van’t Wout JW. Pneumocystis carinii pneumonia in patients without AIDS, 1980 through 1993: An analysis of 78 cases. Arch Intern Med 1995;155:2436-2441. https://www.ncbi.nlm.nih.gov/pubmed/7503602

4. Park JW, Curtis JR, Moon J, et al. Prophylactic effect of trimethoprim-sulfamethoxazole for Pneumocystis pneumonia in patients with rheumatic diseases exposed to prolonged high-dose glucocorticoieds. Ann Rheum Dis 2018;77:664-9. https://www.ncbi.nlm.nih.gov/pubmed/29092853

5. Anevlavis S, Kaltsas K, Bouros D. Prophylaxis for pneumocystis pneumonia (PCP) in non-HIV infected patients. PNEUMON 2012;25, October-December.http://www.pneumon.org/assets/files/789/file483_273.pdf

6. Stern A, Green H, Paul M, Leibovici L. Prophylaxis for pneumocystis pneumonia (PCP) in non-HIV immunocompromised patients (Review). Cochrane data of Systematic Reviews 2014, issue 10. DOI: 10.1002/14651858.CD005590.pub3. https://www.ncbi.nlm.nih.gov/pubmed/25269391

 

When should I consider prophylaxis for Pneumocystis pneumonia (PCP) in my patient on prednisone?

Should Aerococcus urinae growth from the urine of my elderly patient be considered a pathogen?

Although for many years Aerococcus urinae was considered a urinary contaminant, increasingly it is recognized as an emerging pathogen capable of causing not only urinary tract infection (UTI) but also secondary bacteremia and endocarditis, among others.1   

The proportion of patients with aerococcal bacteriuria with symptoms suggestive of UTI ranges from 55-98%.1 So A. urinae can no longer be assumed to be a contaminant, particularly in the presence of symptoms suggestive of UTI.

A. urinae UTI often affects the elderly (median age 79 y) and those with pre-existing urinary tract pathologies, such as prostatic hyperplasia, urethral stricture, renal calculi, and prior urinary tract surgery.2,3 Many patients also have underlying comorbidities such as diabetes, heart disease, dementia, and chronic renal failure.3

One clue to the presence of A. urinae in the urine is its particularly pungent odor reminiscent of that of patients with trimethylaminuria (fish odor syndrome).4

Once you decide you should treat A. urinae, keep in mind that it is NOT predictably susceptible to trimethoprim-sulfamethoxazole, fluoroquinolones, or fosfomycin!  Instead, consider penicillin, ampicillin, cephalosporin, or nitrofurantoin to which most strains are susceptible.5,6.

 

References

  1. Rasmussen M. Aerococcus: an increasingly acknowledged human pathogen. Clin Microbiol Infect 2016;22:22-27. https://www.ncbi.nlm.nih.gov/pubmed/26454061
  2. Tathireddy H, Settypalli S, Farrell JJ. A rare case of aerococcus urinae infective endocarditis. J Community Hosp Intern Med Perspectives 2017; 7:126-129. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5473194/
  3. Higgins A, Garg T. Aerococcus urinae: An emerging cause of urinary tract infection in older adults with multimordidity and urologic cancer. Urology Case Reports 2017;24-25. https://www.ncbi.nlm.nih.gov/pubmed/28435789
  4. Lenherr N, Berndt A, Ritz N, et al. Aerococcus urinae: a possible reason for malodorus urine in otherwise healthy children. Eur J Pediatr. 2014;173:1115-7 https://www.ncbi.nlm.nih.gov/pubmed/24913181
  5. Christensen JJ, Nielsen XC. Aerococcus urinae. Antimicrobe @ http://www.antimicrobe.orgb75.asp , accessed June 14, 2018.
  6. Dimitriadi D, Charitidou C, Pittaras T, et al. A case of urinary tract infection caused by Aerococcus urinae. J Bacteriol Mycol 2016; 2: 00041. https://pdfs.semanticscholar.org/a1cf/048d8444ce054ca9a332f7c2b4a218325ff6.pdf

 

Should Aerococcus urinae growth from the urine of my elderly patient be considered a pathogen?

My patient just developed a fixed drug reaction from ibuprofen. What is the mechanism of this type of skin reaction?

Although its mechanism is not full elucidated, fixed drug eruption (FDE) is thought to result from the drug-induced cytotoxic activation of CD8+ memory T cells.1 ,2

In this context, the culprit medication behaves as a hapten that adheres to basal keratinocytes which in turn results in the recruitment of T cells and inflammation.  However, as the inflammation resolves, CD8+  effector-memory T cells remain in the area in question,  setting the stage for more rapid immunologic reaction when the drug is reintroduced.

Why a systemic drug triggers a reaction only at specific sites in the body is a fascinating question. Prior herpes simplex virus (HSV) infection (eg, on the lips or genitalia) may explain some cases.1 Interestingly, despite the absence of prior herpetic lesions, most patients with FDE are seropositive for HSV. Previously traumatized body sites (e.g. from burns or insect bites) may also create an immune microenvironment conducive to FDE.

The classic presentation of FDE is reappearance of a rash in the genitals, perianal areas, hands, and feet within 30 min to 8 hours of taking the culprit medication.3 Look specifically for NSAIDs, tetracyclines, sulfonamides, and aspirin on the patient’s drug list. 4

References

  1. Shiohara, T. Fixed drug eruption: Pathogenesis and diagnostic tests. Curr Opin Allergy Clin Immunol 2009; 9:316-21. https://www.ncbi.nlm.nih.gov/pubmed/19474709
  2. Butler, DF. Fixed Drug Eruptions. Medscape. http://emedicine.medscape.com/article/1336702-overview#a4. Accessed March 26, 2018.
  3. Korkij W, Soltani K. Fixed drug eruptions: A brief review. Arch Dermatol 1984;120:520. https://www.ncbi.nlm.nih.gov/pubmed/6231004
  4. Oakley, A. Fixed Drug Eruption. https://www.dermnetnz.org/topics/fixed-drug-eruption Accessed March 26, 2018.

 

Contributed by Amir Hossein Ameri, Medical Student, Harvard Medical School

My patient just developed a fixed drug reaction from ibuprofen. What is the mechanism of this type of skin reaction?

My elderly patient on chronic warfarin with recent hospitalization for soft tissue infection is now readmitted with gastrointestinal bleed and a newly-discovered supra-therapeutic INR? Why did her INR jump?

Assuming no recent changes in the dose of warfarin, one potential culprit may be her recent antibiotic exposure. Of the long list of antibiotics associated with elevated INR, quinolones (e.g. ciprofloxacin, levofloxacin), trimethoprim-sulfamethoxazole, macrolides (e.g. azithromycin), and azole antifungals (e.g. fluconazole) are generally thought to carry the highest risk of warfarin toxicity, while amoxacillin and cephalexin may be associated with a more modest risk. 1-3

Other drugs such as amiodarone (Did she have atrial fibrillation during her recent hospitalization?), acetaminophen (Has she been receiving at least 2 g/day for several consecutive days?), and increasing dose of levothyroxine (Was she thought to be hypothyroid recently?) should also be considered.3,4

Also remember to ask about herbal supplements (eg, boldo-fenugreek, dong quai, danshen) that may potentiate the effect of warfarin. 3 Of course, poor nutrition in the setting of recent illness might have also played a role.5

As far as the mechanisms for drug interaction with warfarin, some drugs act as cytochrome p450 inhibitors (thus reducing the metabolism of warfarin), while others influence the pharmacodynamics of warfarin by inhibiting the synthesis or increasing the clearance of vitamin K-2 dependent coagulation factors.3

Antibiotics may increase the risk of major bleeding through disruption of intestinal flora that synthesize vitamin K-2 with or without interference with the metabolism of warfarin through cytochrome p450 isozymes inhibition.

Check out a related pearl on P4P: https://pearls4peers.com/2015/06/25/is-there-anyway-to-predict-a-significant-rise-in-inr-from-antibiotic-use-in-patients-who-are-also-on-warfarin  

 

References

  1. Baillargeon J, Holmes HM, Lin Y, et al. Concurrent use of warfarin and antibiotics and the risk of bleeding in older adults. Am J Med. 2012 February ; 125(2): 183–189. https://www.ncbi.nlm.nih.gov/pubmed/22269622
  2. Juurlink DN. Drug interactions with warfarin: what every physician should know. CMAJ, 2007;177: 369-371. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1942100/pdf/20070814s00018p369.pdf
  3. Ageno W, Gallus AS, Wittkowsky A, et al. Oral anticoagulant therapy: Antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest. 2012;141(2 Suppl):e44S-e88S. doi:10.1378/chest.11-2292.  https://www.ncbi.nlm.nih.gov/pubmed/22315269
  4. Hughes GJ, Patel PN, Saxena N. Effect of acetaminophen on international normalized ratio in patients receiving warfarin therapy. Pharmacotherapy 2011;31:591-7. https://www.ncbi.nlm.nih.gov/pubmed/21923443
  5. Kumar S, Gupta D, Rau SS. Supratherapeutic international normalized ratio: an indicator of chronic malnutrition due to severely debilitating gastrointestinal disease. Clin Pract. 2011;1:e21. doi:10.4081/cp.2011.e21. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3981245

 

Contributed by Rachel Weitzman, Medical Student, Harvard Medical School, Boston, MA.

My elderly patient on chronic warfarin with recent hospitalization for soft tissue infection is now readmitted with gastrointestinal bleed and a newly-discovered supra-therapeutic INR? Why did her INR jump?

Is there anyway to predict a significant rise in INR from antibiotic use in patients who are also on warfarin?

Not really!  Many of the commonly used antibiotics have the potential for increasing the risk of major bleeding through disruption of intestinal flora that synthesize vitamin K-2 with or without interference with the metabolism of warfarin through cytochrome p450 isozymes inhibition.

Although there may be some inconsistencies in the reports, generally quinolones (e.g. ciprofloxacin, levofloxacin), sulonamides (e.g. trimethoprim-sulfamethoxazole), macrolides  (e.g. azithromycin), and azole antifungals (e.g. fluconazole) are thought to carry the highest risk of warfarin toxicity, while amoxacillin and cephalexin may be associated with a more modest risk (1,2).  Metronidazole can also be a culprit (2).

References

1. Baillargeon J, Holmes HM, Lin Y, et al. Concurrent use of warfarin and antibiotics and the risk of bleeding in older adults. Am J Med. 2012 February ; 125(2): 183–189. https://www.ncbi.nlm.nih.gov/pubmed/22269622

2. Juurlink DN. Drug interactions with warfarin: what every physician should know. CMAJ, 2007;177: 369-371. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1942100/pdf/20070814s00018p369.pdf

Is there anyway to predict a significant rise in INR from antibiotic use in patients who are also on warfarin?