Diagnoses Associated With Inpatient Mortality in AS

Cervical spine (c-spine) fractures with associated spinal cord injuries were identified as the leading cause of mortality among hospitalized patients in the U.S. with ankylosing spondylitis (AS), according to data from a nationwide inpatient database published in Arthritis Care & Research.  Researchers found that mechanical falls were the most common causes of c-spine fractures in AS.

Studies investigating causes of mortality in AS have been limited due to relatively low prevalence, and also because cause of death in AS is usually not secondary to AS itself.  To investigate causes of inpatient mortality in AS, Katherine Wysham, MD, of the University of California San Francisco, analyzed patient data from the Nationwide Inpatient Sample (NIS), a dataset of the Healthcare Cost and Utilization Project, the largest publicly available inpatient healthcare database in the U.S.  The NIS contains de-identified hospitalization information, including patient demographics, discharge diagnoses, and inpatient mortality rates.

The NIS was used to identify 12 484 hospital admissions with diagnosis of AS, with 267 deaths during hospitalization between 2007 and 2011. Diagnoses were based on International Classification of Diseases-9 Clinical Modification (ICD9-CM) codes. Clinical Classification Software codes.  

External cause of injury codes were employed to target mechanism of injury into “fall”, “motor vehicle accident”, or “other”. Univariate and multivariate analyses were then performed to identify which variables were associated with inpatient death in patients with c-spine fracture, and to determine if AS was independently associated with it.

C-spine fractures with concomitant spinal cord injuries were associated with the highest odds (OR) for patient death during hospitalization (13.43 [95% Confidence Interval (CI) 8.00-22.55; P<.0001]). Sepsis was associated with a 7.63 OR for increased mortality (95% CI 5.62-10.36; P<.0001).

Other diagnoses found to be associated with mortality in AS included sepsis, pneumonia, and cardiovascular disease.

Mechanical falls were identified as the primary mechanism by which c-spine fractures occurred in hospitalized patients with AS. 

Summary and Clinical Applicability

Vertebral fracture is a well-known complication of AS, and is a contributor to the morbidity associated with disease. This population-based study found that c-spine fracture was associated with the highest OR of inpatient mortality in patients with AS.  

“The high incidence of vertebral fractures and the associated mortality in AS warrant further study… evaluating risk factors such as disease duration, burden of radiographic damage, fall risk, osteoporosis as well as medication usage will be important to further understand the risk factors associated with the outcome of spinal fracture in AS,” the authors concluded. 

Limitations and Disclosures

Due to the use of the national NIS database to obtain data, classifications of multiple hospitalizations of a single patient was not possible. Deaths associated with AS after inpatient discharge from the hospital were also not accounted for. Coding errors may have biased the dataset. 

Reference

Wysham KD, Murray SG, Hills N, Yelin E, Gensler LS. Cervical Spine Fracture and Other Diagnoses Associated with Mortality in Hospitalized Ankylosing Spondylitis Patients. Arthritis Care Res (Hoboken). 2016; Epub ahead of print. Accepted Article, doi: 10.1002/acr.22934