A18.4 vs L52
A18.4 and L52 can never be reported together. ICD-10-CM declares them mutually exclusive with an Excludes1 note, meaning the two conditions cannot occur in the same patient — so exactly one of them is correct for any given encounter.
The official note, declared on L52
tuberculous erythema nodosum (A18.4)
A18.4
Tuberculosis of skin and subcutaneous tissue
Billable
- Chapter 1
- Certain infectious and parasitic diseases
- Section
- A15-A19
Use when the record says
- Erythema induratum, tuberculous
- Lupus exedens
- Lupus vulgaris NOS
- Lupus vulgaris of eyelid
- Scrofuloderma
- Tuberculosis of external ear
Indexed under
- Acnitis (primary)
- Bazin's disease (primary) (tuberculous)
- Lichenoides tuberculosis (primary)
- Scrofulide (primary) (tuberculous)
- Scrofuloderma, scrofulodermia (any site) (primary)
L52
Erythema nodosum
Billable
- Chapter 12
- Diseases of the skin and subcutaneous tissue
- Section
- L49-L54
Indexed under
- Dermatitis › contusiformis (eczematous)
- Erythema, erythematous › induratum (infectional) (inflammation)
- Erythema, erythematous › nodosum (infectional) (inflammation)
- Arthritis, arthritic › due to or associated with › erythema › nodosum (acute) (chronic) (nonpyogenic) (subacute)
- Arthritis, arthritic › in › erythema › nodosum (acute) (chronic) (nonpyogenic) (subacute)
These two codes sit in different chapters of the Tabular List, which is usually the clearest signal that they describe different underlying processes rather than different degrees of the same one.
Excludes1 is not always absolute: where two conditions covered by the note are genuinely unrelated, CMS guidance permits reporting both. Document the reasoning rather than assuming it. More on Excludes1 vs Excludes2 · FY2027