ICD-10-CM 2027
ICD-10 code for connective tissue syndrome
From the official ICD-10-CM alphabetic index entry “Syndrome › connective tissue”. Page updated September 29, 2026.
About coding connective tissue syndrome
The ICD-10-CM code for connective tissue syndrome is M35.9 (Systemic involvement of connective tissue, unspecified). The official index lists 1 more specific code, so check the documentation for details such as type, cause, site or severity before settling on M35.9.
Within M35, choose M35.9 (Systemic involvement of connective tissue, unspecified) only when documentation doesn't support a more specific option: Sjogren syndrome (M35.0), other overlap syndromes (M35.1), Behcet's disease (M35.2), polymyalgia rheumatica (M35.3), diffuse (eosinophilic) fasciitis (M35.4), multifocal fibrosclerosis (M35.5), relapsing panniculitis [Weber-Christian] (M35.6), hypermobility syndrome (M35.7) and 1 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.
More specific connective tissue syndrome codes (official index)
- overlap NEC M35.1 — Other overlap syndromes
Common questions about connective tissue syndrome ICD-10 codes
What is the ICD-10 code for connective tissue syndrome?
- M35.9 — Systemic involvement of connective tissue, unspecified. More specific codes apply when the documentation supports them: M35.1.
What is the ICD-10 code for overlap nec connective tissue syndrome?
- M35.1 — Other overlap syndromes.
Is M35.9 billable?
- Yes. M35.9 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can M35.9 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict M35.9 as a principal diagnosis.
Is M35.9 a CC or MCC?
- No. M35.9 is neither a CC nor an MCC under MS-DRG v44.0.