Pyelonephritis in an Immunocompromised Host Presented as a ...

138 Jul 2010 Vol 3 No.3 North American Journal of Medicine and ScienceIn light of the biopsy findings, he was given an extended (6-week) course of cefprozil. He responded with a completeresolution of leukocyturia, and a month later his serumcreatinine level returned to 106 µmol/L. He continued regularfollow-up at our Out-Patient Clinic.DiscussionUTI/pyelonephritis is one of the most common infections inimmunocompromised hosts and a major source of morbidityand mortality. 2,3 Pathogenic Escherichia coli is by far themost common pathogen, accounting for the vast majority ofUTIs. In our patient, although blood and urine cultures werenegative (possibly related to antibiotic exposure), his clinicaland laboratory presentations, kidney biopsy findings,response to antibiotics, and the absence of other causes forhis symptomatology (negative anaphylaxis workup) indicatedthat he had septic shock secondary to bacterialpyelonephritis.UTI including pyelonephritis is the outcome of interactionbetween the bacteria virulence characteristics and the hostdefense mechanisms. Pathogenic Escherichia coli typicallygain access to the gastrointestinal tract, and from there spreadto the urinary tract and ascend to invade kidneys.Pathogenic Escherichia coli adhere to the uroepitheliumthrough their surface molecule adhesin (hair-like projectionsalso termed p-fimbriae or pyelonephritis-associated pili).Adhesin also decreases IgA transport into the urine resultingin a reduction of local host defense. 8 Althoughpolymorphonuclear cells (PMNs) do not possess adhesinreceptor, they possess receptors binding to another group ofpili of Escherichia coli, type I pili. The binding of PMNs andtype I pili prevents bacteria adhesion to the uroepithelia.Although rare strains of Escherichia coli can shed their pili 9thereby circumventing the effects of PMNs, in mostcircumstances, PMNs bind bacteria and protect hosts frominfection. The pathogen in the current case was mostly likelyEscherichia coli, as numerous epidemiologic studiesindicating that they are the most common cause of UTI inimmunocompromised hosts. 10With regard to the host defense, our patient had severaldeficiencies. First and perhaps most important, he had beenunder heavy immunosuppression for 6 months. Drug-inducedmarrow suppression prevented a robust leukemoid reaction tothe infection. Second, secretory IgAs are known toparticipate in the maintenance of mucosal surface immunehomeostasis and confer protection against pathogencolonization. Secretory IgAs also can neutralize bacteria PLS(important for Escherichia coli pathogenesis) independent ofgranulocyte cells or T-cells. Our patient had IgAnephropathy, which is pathogenetically related to defects inO-linked glycosylations. Such defects can alter the chargecharacteristics of IgA1 molecules. IgA1 with incomplete O-galactosylation also tends to self-aggregate, 9 thereby maydiminish its physiological functions. Third, our patient hasdiabetes, which is one of the metabolic factors known toenhance bacterial invasiveness within urinary tract inimmune compromised hosts.Classically, history and physical examination are essential inidentifying the existence and source of infection. In thispatient, although he appeared in shock, a diagnosis ofinfection as an etiology of his presentation was called intoquestion because (1) by history, he had been on TMP/SMXprophylaxis since the start of the immunosuppressivetreatment and he did not show any focal (urinary) symptoms(might be related to the insufficient local leukemoid reaction,at least initially), and (2) on examination, he did not haveflank pain or abdominal tenderness. This atypicalpresentation created a diagnostic dilemma.Immunosuppressive therapy can mask the clinicalmanifestations of infection. Our patient did not haveleukocytosis at his initial presentation to the local hospital,despite sepsis-like presentation. This is likely related to themarrow suppressive effect of cyclophosphamide. In line withthis assumption, his serum leukocyte counts (and urineleukocytes) were increased in the succeeding days as moretime elapsed from the last dosage of cyclophosphamide,consistent with a gradual recovery of leukemoid response toinfection. Although the steroid administration during hishospital stay could have contributed to the leukocytosis, itwas unlikely to have been a major factor because theleukocytosis on admission preceded the initiation of stressdosesteroids. Thus, the initial lack of leucocytosis was likelyrelated to drug-associated marrow suppression. Incidentally,this case also served to dispel the notion that patients onTMP/SMX prophylaxis would not be at risk for UTI. Ourpatient developed pyelonephritis while on TMP/SMX, andrecent studies also show that over 70% uropathogenicbacteria are insensitive or resistant to TMP/SMX 11 .Although infection, given its potential fatality, should bedoggedly pursued, it is plausible to include multiplediagnostic considerations. The atypical presentations in thiscase led to seeking alternative explanations, such as pseudosepsisdue to drug reaction.Azathioprine is an imidazole derivative of 6-mercaptopurine.The allergic-type reactions have been described as a rare anddose-independent event occurring within days to weeksfollowing the drug introduction. 6 The reactions can rangefrom pancreatitis, hepatitis, skin rash, fever, arthralgias,malaise, diarrhea and abdominal pain to anaphylactic shock.The anaphylactic reaction/shock is characterized by abruptonset of headache, fever, hypotension and leukocytosis. 5,6Although our patient’s presentation fit well with thisdescription, his laboratory studies did not. In a typicalanaphylactic reaction, circulating mast cells are acutelyactivated, releasing a host of vasoactive mediators includingtryptase, histamine, and prostaglandin D2. Serum and urinelevels of these mediators and their metabolites, N-Methylhistamine and 11β-Prostaglandin F 2α , are expected tobe massively and simultaneously elevated. Our patient had anisolated elevation of 11β-Prostaglandin F 2α , inconsistent withanaphylactic reaction. 7 In fact, the isolated 11β-ProstaglandinF 2α elevation (to the level comparable to that in our patient)can be seen in physiologic conditions during normal labor 12or sleep 13 . Under these circumstances 11β-Prostaglandin F 2α