2027 ICD-10-CM Diagnosis Code A50.55Late congenital syphilitic arthropathy
ICD-10-CM Codes›A00–B99›A50-A64›A50
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 92
- Chronic Condition
A50.55 is a billable ICD-10-CM diagnosis code for late congenital syphilitic arthropathy. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 867 through 869. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 79 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified bone disease and musculoskeletal deformities, Perinatal infections, and Sexually transmitted infections (excluding HIV and hepatitis).
For Medicare Advantage risk adjustment, A50.55 maps to CMS-HCC Category 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis) under the V28 model, adding a risk factor of about 0.479 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
A50.55 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.
Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to A50.55: its own notes plus those printed at block A50-A64 and Chapter 1. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- diseases generally recognized as communicable or transmissible
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
- human immunodeficiency virus [HIV] disease (B20)
- carrier or suspected carrier of infectious disease (Z22.-)
- certain localized infections - see body system-related chapters
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
- infectious and parasitic diseases specific to the perinatal period (P35-P39)
- influenza and other acute respiratory infections (J00-J22)
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify resistance to antimicrobial drugs (Z16.-)
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name A50.55, its category, or a range that includes it.
Applicable To 1
These notes mention A50.55.
- O98.1 Syphilis complicating pregnancy, childbirth and the puerperium
Excludes1 3
These codes carry an Excludes1 note naming A50.55: they are not reported together with it, unless the two conditions are unrelated.
- K00.2 Abnormalities of size and form of teethabnormalities of teeth due to congenital syphilis (A50.5) names A50.5, which includes this code
- K00.4 Disturbances in tooth formationHutchinson's teeth and mulberry molars in congenital syphilis (A50.5) names A50.5, which includes this code
- Q67.4 Other congenital deformities of skull, face and jawsyphilitic saddle nose (A50.5) names A50.5, which includes this code
Excludes2 3
These codes carry an Excludes2 note naming A50.55: its condition is not part of those codes, and both may be reported when the patient has both.
- Block P35-P39 Infections specific to the perinatal periodcongenital syphilis (A50.-) names A50.-, which includes this code
- P37 Other congenital infectious and parasitic diseasescongenital syphilis (A50.-) names A50.-, which includes this code
- Block A65-A69 Other spirochetal diseases
Code First 6
These codes say to code first a condition named in the note, and A50.55 is one of the conditions named.
- I52 Other heart disorders in diseases classified elsewherecongenital syphilis (A50.5) names A50.5, which includes this code
- J99 Respiratory disorders in diseases classified elsewherecongenital syphilis (A50.-) names A50.-, which includes this code
- K23 Disorders of esophagus in diseases classified elsewherecongenital syphilis (A50.5) names A50.5, which includes this code
- K77 Liver disorders in diseases classified elsewherecongenital syphilis (A50.0, A50.5) names A50.5, which includes this code
- M02 Postinfective and reactive arthropathiescongenital syphilis [Clutton's joints] (A50.5) names A50.5, which includes this code
- N08 Glomerular disorders in diseases classified elsewherecongenital syphilis (A50.5) names A50.5, which includes this code
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Arthropathy See Also: Arthritis; M12.9
Hydrarthrosis See Also: Effusion, joint;
congenital A50.55
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Syphilis, Congenital
syphilis acquired in utero and manifested by any of several characteristic tooth (hutchinson's teeth) or bone malformations and by active mucocutaneous syphilis at birth or shortly thereafter. ocular and neurologic changes may also occur.
Patient EducationClinical
Infectious Arthritis
Most kinds of arthritis cause pain and swelling in your joints. Joints are places where two bones meet, such as your elbow or knee. Infectious arthritis is an infection in the joint. The infection comes from a bacterial, viral, or fungal infection that spreads from another part of the body. Symptoms of infectious arthritis include:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert A50.55 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About A50.55Overview
What is the ICD-10 code for late congenital syphilitic arthropathy?
The ICD-10-CM code for late congenital syphilitic arthropathy is A50.55 (sometimes written as A5055). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is A50.55 (Other late congenital syphilis, symptomatic) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report late congenital syphilitic arthropathy on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does A50.55 group to?
When late congenital syphilitic arthropathy is the principal diagnosis on an inpatient stay, it groups to MS-DRG 867, 869, 868, with relative weights from 0.6784 to 2.1855 depending on complications. Higher weights mean higher Medicare reimbursement.
Is A50.55 a CC or MCC?
CMS lists A50.55 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 79 closely related codes in its exclusion list.
Can A50.55 be reported with N34.1?
Not as a rule. The Excludes1 note at block A50-A64, which applies to A50.55, lists "nonspecific and nongonococcal urethritis (N34.1)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
What HCC is A50.55?
A50.55 (late congenital syphilitic arthropathy) maps to CMS-HCC Category 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis), commonly written as HCC 92, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 39 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.
Does A50.55 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, A50.55 adds a risk adjustment factor of about 0.479 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.471 to 0.632 depending on the payment segment). HCC 92 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 92 category page.
