M35.9 — Systemic involvement of connective tissue, unspecified

BillableUnspecified

Is M35.9 billable?

Yes, but M35.9 is an unspecified code. M35.9 is a valid, billable ICD-10-CM code for encounters from October 1, 2026 through September 30, 2027. However, M35.9 is an unspecified or catch-all code. Payers apply additional scrutiny to unspecified codes and many deny them when the medical record supports a more specific option, so check the documentation before selecting M35.9 — the more specific alternatives are listed below.

More specific alternatives

M35.9 at a glance

Code	M35.9
Description	Systemic involvement of connective tissue, unspecified
Billable	Yes
Code set	ICD-10-CM FY2027
Valid for encounters	October 1, 2026 – September 30, 2027

Which MS-DRGs does M35.9 group to?

M35.9 sits in MDC 08 and helps define the logic of 3 MS-DRGs (version 44, FY2027). Which one a stay actually groups to also depends on procedures and secondary diagnoses.

545Connective Tissue Disorders with MCCmedical
546Connective Tissue Disorders with CCmedical
547Connective Tissue Disorders without CC/MCCmedical

How is M35.9 listed in the Alphabetic Index?

These are the routes through the Alphabetic Index that lead to M35.9. They show the wording a clinician may have documented, which often differs from the Tabular description.

Collagenosis, collagen disease (nonvascular) (vascular)
Dyscollagenosis
Ataxia, ataxy, ataxic › gluten
Autoimmune › disease
Disease, diseased › autoimmuneNOS
Disease, diseased › collagen NOS
Disease, diseased › connective tissue, systemic
Disease, diseased › mesenchymal
Skin › hidebound
Syndrome › connective tissue
Polyneuropathy › in › collagen vascular disease NEC (peripheral)
Polyneuropathy › in › systemic › connective tissue disorder (peripheral)

Inclusion terms

Alternative wording in documentation that is classified to M35.9.

Autoimmune disease (systemic) NOS
Collagen (vascular) disease NOS

Excludes1 — never code together — inherited from M30-M36

The conditions below can never be reported together with M35.9 on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.

autoimmune disease, single organ or single cell-type -code to relevant condition category

Excludes1 — never code together — inherited from M35

The conditions below can never be reported together with M35.9 on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.

reactive perforating collagenosis (L87.1)

Excludes2 — not included here — inherited from Chapter 13

The conditions below are not part of M35.9, but a patient may have both at the same time. When documentation supports it, M35.9 and the excluded code may both be reported.

arthropathic psoriasis (L40.5-)
certain conditions originating in the perinatal period (P04-P96)
certain infectious and parasitic diseases (A00-B99)
compartment syndrome (traumatic) (T79.A-)
complications of pregnancy, childbirth and the puerperium (O00-O9A)
congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
endocrine, nutritional and metabolic diseases (E00-E88)
injury, poisoning and certain other consequences of external causes (S00-T88)
neoplasms (C00-D49)
symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

How long has M35.9 existed?

M35.9 has been in ICD-10-CM since at least FY2016, the earliest fiscal year on record here.

Derived from the official order files for FY2016–FY2026. FY2017 and FY2020 publish no order file, so those years are not covered.