M45.9 — Ankylosing spondylitis of unspecified sites in spine

BillableUnspecified

Is M45.9 billable?

Yes, but M45.9 is an unspecified code. M45.9 is a valid, billable ICD-10-CM code for encounters from October 1, 2026 through September 30, 2027. However, M45.9 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 M45.9 — the more specific alternatives are listed below.

More specific alternatives

M45.9 at a glance

Code	M45.9
Description	Ankylosing spondylitis of unspecified sites in spine
Billable	Yes
Code set	ICD-10-CM FY2027
Valid for encounters	October 1, 2026 – September 30, 2027

Which MS-DRGs does M45.9 group to?

M45.9 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 M45.9 listed in the Alphabetic Index?

These are the routes through the Alphabetic Index that lead to M45.9. They show the wording a clinician may have documented, which often differs from the Tabular description.

Spondylitis › ankylosing (chronic)
Iridocyclitis › in › ankylosing spondylitis
Spondylitis › ankylosing › with lung involvement (chronic)

Excludes1 — never code together — inherited from M45

The conditions below can never be reported together with M45.9 on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.

arthropathy in Reiter's disease (M02.3-)
juvenile (ankylosing) spondylitis (M08.1)

Excludes2 — not included here — inherited from Chapter 13

The conditions below are not part of M45.9, but a patient may have both at the same time. When documentation supports it, M45.9 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)

Excludes2 — not included here — inherited from M45

The conditions below are not part of M45.9, but a patient may have both at the same time. When documentation supports it, M45.9 and the excluded code may both be reported.

Behçet's disease (M35.2)

How long has M45.9 existed?

M45.9 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.

Which conditions are coded to M45.9?

ICD-10 code for Iridocyclitis