ICD-10 code for ankylosing spondylitis

The ICD-10-CM code for ankylosing spondylitis is M45.9 (Ankylosing spondylitis of unspecified sites in spine). The official index lists 19 more specific codes, so check the documentation for details such as type, cause, site or severity before settling on M45.9.

Within M45, choose M45.9 (of unspecified sites in spine) only when documentation doesn't support a more specific option: of multiple sites in spine (M45.0), of occipito-atlanto-axial region (M45.1), of cervical region (M45.2), of cervicothoracic region (M45.3), of thoracic region (M45.4), of thoracolumbar region (M45.5), lumbar region (M45.6), of lumbosacral region (M45.7) and 2 more.

It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.

In MS-DRG v44.0, it is part of the grouping logic for DRG 545 (Connective Tissue Disorders with MCC, relative weight 2.3892), DRG 546 (Connective Tissue Disorders with CC, relative weight 1.1745) and DRG 547 (Connective Tissue Disorders without CC/MCC, relative weight 0.7526), in MDC 08 (Diseases and Disorders of the Musculoskeletal System and Connective Tissue), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.