Bacteriology of Inflamed and Uninflamed Epidermal Inclusion Cysts
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STUDY Bacteriology of Inflamed and Uninflamed Epidermal Inclusion Cysts Dayna G. Diven, MD; Susan E. Dozier, MD; Diane J. Meyer, MD; Edgar B. Smith, MD Objective: To determine whether inflamed and unin- Results: The 2 groups did not differ significantly with flamed epidermoid cysts differ in the number and/or type respect to number of bacterial isolates, “no growth” of bacteria inhabiting them. cultures, and aerobic, anaerobic, or potential patho- gens cultured. Design: A controlled study. We obtained aerobic and anaerobic bacterial culture specimens from 25 inflamed and 25 uninflamed epidermoid cysts. Conclusions: The microbiological milieu of inflamed epi- dermoid cysts is similar to that of uninflamed cysts. Pos- Setting: A university medical center. sible mechanisms for inflammation are discussed. Patients: Nonimmunocompromised adults without re- cent systemic use of antibiotics. Arch Dermatol. 1998;134:49-51 HE EPIDERMAL inclusion cyst out that this was not a controlled study yet is a common acquired skin concedes that S aureus likely played a role cyst. When such cysts be- in some of the infected cysts. come inflamed they are of- Our study was undertaken to better ten referred to as infected define the microbiological milieu of the in- Tand treated by incision and drainage and flamed and uninflamed epidermal inclu- often by administering systemic antibiot- sion cyst. ics. The presupposition that infection plays a significant role in the inflammatory pro- RESULTS cess has never been studied in a con- trolled manner. Only 2 studies have ad- Twenty-five inflamed and 25 uninflamed dressed this issue in any manner. In 1977 cysts were cultured. Patients ranged in age Leppard et al1 cultured 11 uninflamed epi- from 21 to 78 years. The mean age of pa- dermoid cysts and found that 73% grew tients with inflamed cysts was 49 years (age common skin commensals, including range, 21-78 years) and the mean age for Staphylococcus epidermidis, anaerobic those with uninflamed cysts was 46 years gram-positive cocci, and Corynebacte- (age range, 22-74 years). The percentage rium acnes. In 1980 Brook2 cultured 231 of women was 40% in the inflamed and “epidermal cyst abscesses,” 192 of which 32% in the uninflamed cyst groups. The yielded bacterial growth. One hundred location of the cysts was similar in both eight of the 192 grew anaerobic organ- groups (Table 1). isms (predominantly Peptostreptococcus Each group did not differ signifi- species and Bacteroides species) and 135 cantly with respect to number of isolates, of 192 grew aerobic organisms (predomi- average number of isolates per patient, no nantly Staphylococcus aureus). Twenty- growth cultures, aerobes cultured, anaer- three patients in this study had previous obes cultured, normal flora, or potential antimicrobial therapy. Brook stressed the pathogens (Table 2 and Figures 1 From the Department importance of anaerobic bacteria and S au- through 3). The majority of positive cul- of Dermatology, University reus in the infected cysts and recom- tures were quantitated at 2+ or 3+. The of Texas Medical Branch, Galveston (Drs Diven and mended surgical drainage as the treat- positive cultures from the inflamed cysts Smith), Austin Regional Clinic, ment of choice with the addition of were quantified as follows: 1+ growth Austin, Tex (Dr Dozier), and antimicrobials such as cefoxitin or a com- (n=6), 2+ (n=11), 3+ (n=12), and 4+ Marshfield Clinic, Chippewa bination agent of imipenem-cilastatin so- (n=3). The positive cultures from the un- Falls, Wis (Dr Meyer). dium in selected cases. Valentine3 points inflamed cysts were quantified as fol- ARCH DERMATOL / VOL 134, JAN 1998 49 ©1998 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/24/2021 Table 1. Location of Inflamed and PATIENTS AND METHODS Uninflamed Epidermoid Cysts Epidermoid Cyst, No. Patients were recruited from the outpatient dermatol- ogy service at the University of Texas Medical Branch Location Inflamed Uninflamed at Galveston. All patients were 18 years or older with Face 5 8 an epidermal inclusion cyst that was being removed for Neck or scalp 5 4 therapeutic or cosmetic reasons. Any patient who had Trunk 11 11 received antibiotics within 1 month of their proce- Extremities 2 2 dure or who was immunosuppressed was excluded. Intertriginous 1 0 An inflamed cyst was defined as a cyst known to present for months to years that subsequently devel- oped fluctuance and erythema and contained a local- Table 2. Organisms Cultured From Epidermoid Cysts ized collection of purulent material in addition to kera- tin debris on incision. An uninflamed cyst was defined as an intradermal nodule without any evidence of in- Epidermoid Cyst, No. flammation that yielded a cheesy keratinous material. Organism Inflamed Uninflamed The overlying skin was prepared with povi- done iodine or chlorhexidine gluconate, then iso- Aerobes Coagulase-negative staphylococcus 16 13 propyl alcohol; 1% lidocaine was administered lo- Diphtheroids 4 4 cally. Cysts were incised with a sterile surgical blade Staphylococcus aureus 21 and then a sterile swab was inserted into the cyst. One a-Hemolytic streptococcus 0 1 swab was reinserted into the standard aerobic trans- Proteus 21 port media (Culterette II Collection and Transport Enterococcus 11 System, Becton Dickinson & Co, Cockeysville, Md) Gram-negative bacilli 0 1 and the other into anaerobic transport media. Anaerobes Specimens were processed routinely by the Uni- Propionibacterium versity of Texas Medical Branch microbiology labo- acnes 23 ratory and plated within 1 hour after arrival onto the Species 3 1 following media: sheep blood agar, chocolate agar, co- Peptostreptococcus listin-nalidixic acid agar, MacConkey agar, Brucella magnus 44 blood agar with heme and vitamin K, blood agar with asaccharolyticus 21 kanamycin sulfate, and vancomycin and thioglyco- Other 1 2 late broth (the latter 3 are anaerobic media). Plates were Pseudomonas incubated at 35°C in 5% to 10% carbon dioxide. An magnus 10 anaerobic chamber was used to incubate the plates for asaccharolyticus 11 anaerobic growth. Microorganisms were identified us- Bacteroides ureolyticus 01 ing the standard methods of Gram stain, aerotoler- Actinomyces meyeri 01 ance, and Rapid ANA (antinuclear antibody) System israelii 01 (Innovative Diagnostic Systems LP, Norcross, Ga) II. Gram-positive cocci 1 0 The Manual of Clinical Microbiology4 was used as a ref- erence. No identification of species was performed for coagulase-negative staphylococci, diphtheroids, en- 40 Inflamed terococci, viridans streptococci, or Bacillus species. Uninflamed Statistical analysis was performed to test for the 35 differences in the proportions of isolated organisms 30 across the 2 groups using the test 25 pˆ 1−pˆ 2 Z = , 20 1 1 ( ) p 1−p + No. of Isolates 15 ! Fn1 n2G 10 where z is distributed approximately and pˆ is an es- timate of the common parameter defined as the sum 5 of the specific organism count from both groups di- 0 vided by the sum of the total number of isolates from Total Aerobic Anaerobic both groups. Figure 1. Number of isolates from inflamed and uninflamed cysts. flamed cysts and 13 of 22 uninflamed cysts of the aerobic positive cultures). Staphylococcus aureus was infre- lows: 1+ (n=4), 2+ (n=16), 3+ (n=11), and no 4+ growth. quently seen, being identified in 2 inflamed cysts and 1 No discernible pattern was seen between the 2 groups uninflamed cyst. Among the 14 positive anaerobic cul- or between species in their quantity. tures in each group of 25 cysts, Peptostreptococcus was the Coagulase-negative staphylococcus was the most fre- most commonly identified genus, isolated from 7 speci- quently cultured organism in both groups (16 of 25 in- mens in both the inflamed and uninflamed cyst groups. ARCH DERMATOL / VOL 134, JAN 1998 50 ©1998 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/24/2021 18 dis activated C5a. No in vivo experiments have been per- Inflamed Uninflamed formed using epidermoid cyst contents. 16 Also unanswered is why the cyst ruptures in the first 14 place. Is it induced by trauma or is there some other ini- 12 tiating event? We did not study the conditions within the s e t a O l 10 cyst, for example the pH or p 2. Does this affect any bac- o s I f teria that might be present? o 8 . o The mainstay of therapy of the inflamed cyst has been N 6 incision and drainage, with or without the use of sys- 2 4 temic antibiotics. Brook recommends drainage and use 2 of broad-spectrum systemic antibiotics to cover for both staphylococcus and anaerobic organisms in selected cases. 0 7 Either Both Aerobic Anaerobic Ho and McLean recommend that “a fluctuant, prob- ably infected cyst should be incised, drained, and cul- Figure 2. Cultures from inflamed and uninflamed cysts exhibiting no growth. tured; if there is no improvement, antibiotic treatment 8 25 should be started.” Young and Mathes recommend in- Inflamed Uninflamed cision and drainage alone for an “acutely infected cyst.” Would the inflamed cyst resolve without any treat- 20 ment? If the organism is not significantly contributing to the inflammation, then would use of antibiotics with s e t 15 known anti-inflammatory properties, such as erythro- a l o 9 s I mycin or tetracycline, alter the clinical course? It would f o . o 10 be interesting to perform a 4-armed controlled study on N the natural course of the inflamed epidermoid cyst with and without incision and drainage and with or without 5 the use of systemic antibiotics. In summary, we found no apparent difference in the 0 Normal Flora Pathogens microbiological milieu of inflamed and uninflamed epi- dermoid cysts. We hope this study generates a renewed in- Figure 3. Normal flora vs potential pathogens cultured from inflamed and uninflamed cysts.