M35.4 identifies diffuse (eosinophilic) fasciitis, a rare systemic fibrosing disorder characterized by inflammatory thickening of the deep fascia with associated peripheral eosinophilia, classified under other systemic involvement of connective tissue.

Documentation tips

What should appear in the chart to support M35.4.

Source · Editorial brief grounded in 5 cited references ↓

• Document 'eosinophilic fasciitis,' 'diffuse fasciitis,' or 'Shulman syndrome' explicitly — generic 'fasciitis' defaults to M72.9 (unspecified fibroblastic disorder), not M35.4.
• Record peripheral eosinophilia lab results (CBC with differential) and any biopsy findings confirming deep fascial inflammation to support the systemic connective tissue diagnosis.
• Note which joints are affected and the degree of mobility restriction — this documentation underpins medical necessity for physical therapy or rehabilitation referrals under CMS A57311.
• If the patient has overlapping morphea features, document the treating physician's clinical determination of primary diagnosis, since eosinophilic fasciitis and morphea share histopathologic features and the distinction affects coding.
• Document any prior treatment trials (e.g., corticosteroids) and response, particularly when requesting home health or PT services that require medical necessity justification.

Related CPT procedures

Procedure codes commonly billed with M35.4. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

Common coding pitfalls

The recurring mistakes coders make with M35.4 and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

• Assigning M72.8 (Other fibroblastic disorders) for eosinophilic fasciitis — M35.4 is explicitly excluded from M72.8 by a Type 1 Excludes note; the two codes cannot be used together.
• Defaulting to M72.9 (Fasciitis NOS) when the physician documents 'diffuse fasciitis' without the word 'eosinophilic' — if the clinical record supports Shulman syndrome, M35.4 is the correct code.
• Confusing M35.4 with plantar fasciitis (M72.2), necrotizing fasciitis (M72.6), or nodular fasciitis (M72.4) — these are distinct entities with separate codes under a different parent category.
• Failing to code relevant comorbid systemic conditions (e.g., hematologic abnormalities sometimes associated with eosinophilic fasciitis) as additional diagnoses when documented.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

Other billable codes under M35 (laterality / anatomic variants).