Abstract
This study examines the incidence of a patient developing appendicitis within 1 week after undergoing a colonoscopy vs during the following 51 weeks.
Appendicitis can occur after a patient undergoes a colonoscopy, but because both are common, it is unclear whether a colonoscopy increases appendicitis risk. We hypothesized that patients develop appendicitis more frequently within 1 week after undergoing a colonoscopy than during the following 51 weeks.
Methods
After obtaining approval and a waiver of informed consent from the University of North Dakota and Fargo Veterans Affairs Medical Center institutional review boards, we identified 392 485 veterans from US Department of Veterans Affairs administrative data with a screening colonoscopy Current Procedural Terminology (CPT) code between January 2009 and June 2014, excluding sigmoidoscopy or incomplete colonoscopy codes. We sought over the following year a CPT code for appendectomy, an International Classification of Diseases, Ninth Revision (ICD-9) code for appendicitis, both CPT and ICD-9 codes, or the appendectomy CPT code with a discharge diagnosis of appendicitis. We calculated the incidence rate ratio (IRR) for appendicitis within 1 week after undergoing a colonoscopy and for the following 51 weeks. χ2 Statistics and 95% confidence intervals were calculated.
Results
Appendicitis or an appendectomy were coded more frequently 1 week after a colonoscopy than during the following 51 weeks (Table). Age subgrouping did not change this, and appendicitis was not increased in weeks 2 to 4 (data not shown). By contrast, appendectomy was not increased 1 week after a bronchoscopy, knee replacement procedure, cataract surgery, or knee arthroscopy in the cohort (Table).
Table. Incidence of Appendicitis or Appendectomy Among Veterans Undergoing a Prior Procedure.
| Analysis Strategy | Prior Procedure | No. of Patients Undergoing Prior Procedure | Week 1 | Weeks 2-52 | Incidence Rate Ratio (95% CI) | P Value by χ2 |
|---|---|---|---|---|---|---|
| Appendicitis ICD-9 codes | Colonoscopy | 392 485 | 26 | 175 | 7.6 (4.8-11.5) | <.001 |
| Appendectomy CPT codes | Colonoscopy | 392 485 | 19 | 112 | 8.7 (5.1-14.2) | <.001 |
| Both ICD-9 and CPT codes | Colonoscopy | 392 485 | 12 | 82 | 7.5 (3.7-13.8) | <.001 |
| Appendectomy CPT codes with appendectomy discharge diagnosis | Colonoscopy | 392 485 | 10 | 79 | 5.7 (2.6-11.0) | <.001 |
| Appendectomy CPT codes | Bronchoscopy | 16 761 | 1 | 9 | 5.7 (0.13-41.1) | .09 |
| Appendectomy CPT codes | Total knee replacement | 19 669 | 0 | 12 | 2.1 (0-22.7) | .68 |
| Appendectomy CPT codes | Cataract | 96 393 | 0 | 49 | 1.1 (.5-2.1) | .57 |
| Appendectomy CPT codes | Knee arthroscopy | 14 272 | 0 | 14 | 1.8 (0-19.1) | .76 |
| Appendectomy CPT codes with chart validation | Colonoscopy | 392 485 | 12 | 79 | 6.8 (3.4-12.6) | <.001 |
| Appendectomy CPT codes with medical record validation and deletion of simultaneous symptoms | Colonoscopy | 392 485 | 7 | 79 | 4.5 (1.8-9.8) | <.001 |
Abbreviations: CPT, Current Procedural Terminology; ICD-9, International Classification of Diseases, Ninth Revision.
Recognizing the challenges of administrative data, we reviewed records from each patient that were CPT-coded for appendectomy. Eliminating patients with appendiceal neoplasms, incidental appendectomies, or no appendectomy in the operative note, we included only patients with surgical and histologic findings that were consistent with appendicitis except for 2 patients outside the first week with clear operative descriptions of acute appendicitis but unavailable pathology reports. Only 12 patients (74%) who were administratively identified as having undergone an appendectomy actually developed appendicitis 1 week after undergoing a colonoscopy. None had appendiceal or cecal biopsies, appendicoliths, or perforated appendicitis. Seventy-nine administratively identified patients (77%) actually had appendicitis over the following 51 weeks. Considering only validated patients from the CPT-based strategy yielded an IRR of 6.8 (95% CI, 3.4-12.6) for appendicitis within a week after colonoscopy (P < .001). Five patients (42%) with appendicitis in week 1 had preexisting symptoms that were investigated by a colonoscopy. Even excluding these yielded an IRR of 4.5 (95% CI, 1.8-9.8; P < .001).
Discussion
Although “healthy user biases” can select individuals who are more likely to use subsequent health care for other reasons, these biases seem unlikely to explain our results because we compared appendicitis 1 week after a colonoscopy with subsequent appendicitis in the same individuals. Nor is appendicitis a diagnosis like hypertension that would be more likely to be an incidental finding on a precolonoscopy history and physical examination. Patients seek medical attention more frequently after undergoing a colonoscopy for colonoscopy-related complaints including bleeding, bloating, and pain, so one could hypothesize that an increased likelihood of complaining of abdominal symptoms might increase the likelihood of diagnosing appendicitis, but all of the index cases of appendicitis in the final analysis were pathologically confirmed, so these were not false-positive diagnoses. Appendicitis may sometimes resolve spontaneously, but the rate at which this occurs is difficult to distinguish from the resolution of abdominal pain during conservative management that was not appendicitis. Older studies that reported frequent nonsurgical resolutions used antibiotics that effectively treat much appendicitis.
While the actual IRR may differ and absolute risk is low, these results suggest that undergoing a colonoscopy predisposes patients to appendicitis within 1 week. The mechanism of this effect awaits elucidation. One patient developed symptoms after cleanout before the procedure. Some bowel preparations can precipitate ischemia or alter the microbiome, so the effect of bowel preparation also warrants exploration. Further mechanistic studies may identify patients who are at higher risk or elements of the bowel preparation or procedure that could be changed to decrease the risk. In the interim, however, these results suggest that there is increased concern for the development of appendicitis among patients with persistent right lower quadrant pain after undergoing a colonoscopy.
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