ICD-10 Code Q78.1: Polyostotic fibrous dysplasia

Key Takeaways

ICD-10 Code Q78.1 (Polyostotic Fibrous Dysplasia) is a billable, specific ICD-10-CM code valid for FY2026 claims.

Inclusion terms cover McCune-Albright syndrome and café au lait spots, but endocrine manifestations may require additional codes.

Q78.1 sits under parent code Q78 (Other Osteochondrodysplasias), which carries Type 2 Excludes notes.

Pabau’s claims management software supports accurate diagnostic code submission to reduce denials.

ICD-10 Code Q78.1: Definition and clinical description

Most billing denials for congenital bone disorder diagnoses trace back to a single problem: coders assign a non-specific parent code when a billable child code exists. Congenital condition diagnosis codes follow the same hierarchy logic, and ICD-10 Code Q78.1 is no exception. This reference covers billability, synonyms, code hierarchy, documentation requirements, and common coding scenarios for Q78.1.

Q78.1 is a billable, specific ICD-10-CM code that identifies polyostotic fibrous dysplasia (PFD), a congenital skeletal disorder in which normal bone tissue is replaced by fibrous tissue across multiple skeletal sites. According to the CDC/NCHS ICD-10-CM web tool, Q78.1 is valid for dates of service from October 1, 2025 through September 30, 2026 (FY2026) and carries no retirement flag. It falls within Chapter Q00-Q99 (Congenital Malformations, Deformations and Chromosomal Abnormalities) under block Q65-Q79 (Congenital Malformations of the Musculoskeletal System).

Is ICD-10 Code Q78.1 billable?

Yes. Q78.1 is a billable and specific ICD-10-CM code. It can be used directly on insurance claims and HIPAA-covered transactions without requiring a more specific subcategory, because no further decimal subdivisions exist beneath Q78.1 in the current code set.

Under HIPAA, covered entities must use ICD-10-CM codes for all electronic health care claims. Using the non-specific parent Q78 instead of Q78.1 when the polyostotic form is documented will trigger specificity edits and likely result in a claim denial. The CMS ICD-10 codes page lists Q78.1 in its annual update files with no indication of change for FY2026.

What is polyostotic fibrous dysplasia?

Polyostotic fibrous dysplasia is a non-inherited skeletal condition caused by a postzygotic mutation in the GNAS1 gene. Normal bone marrow is replaced by fibrous connective tissue at multiple skeletal sites simultaneously. The word “polyostotic” refers to involvement of more than one bone, distinguishing it from monostotic fibrous dysplasia (a single-bone variant) which does not share the Q78.1 code.

Clinical presentations range from mild (incidental radiographic findings) to severe (pathological fractures, limb deformity, skull base involvement). When PFD occurs alongside endocrine dysfunction and café au lait skin lesions, the triad is known as McCune-Albright syndrome, which is listed as an inclusion term under Q78.1. ICD-10 coding for chronic conditions often involves this kind of inclusion-term nuance, where a syndrome is captured under a single code that technically represents one of its components.

Inclusion terms and synonyms

The official ICD-10-CM tabular list includes the following synonyms and inclusion terms for Q78.1:

• Polyostotic fibrous dysplasia
• McCune-Albright syndrome
• Café au lait spots (as a component of the syndrome)

Coders should note that “café au lait spots” as an isolated skin finding without confirmed fibrous dysplasia would not be coded Q78.1. The inclusion applies when café au lait spots are documented in the context of fibrous dysplasia or McCune-Albright syndrome. Verify inclusion terms against the official WHO ICD-10 browser or the NCHS tabular list for the most current guidance.

ICD-10 Code Q78.1 hierarchy and adjacent codes

Understanding the code hierarchy helps coders select the right level of specificity and apply parent-code notes correctly. Q78.1 sits within a three-level hierarchy.

Sibling codes within Q78

Several codes share the Q78 parent category. Understanding these sibling codes prevents miscoding when documentation is ambiguous about the specific type of osteochondrodysplasia.

• Q78.0: Osteogenesis imperfecta (brittle bone disease)
• Q78.1: Polyostotic fibrous dysplasia (ICD-10 Code Q78.1) – this code
• Q78.2: Osteopetrosis
• Q78.3: Progressive diaphyseal dysplasia
• Q78.4: Enchondromatosis
• Q78.6: Multiple congenital exostoses
• Q78.8: Other specified osteochondrodysplasias

There is no Q78.5 in the current ICD-10-CM tabular list. Coders encountering “fibrous dysplasia” in documentation without a qualifier (monostotic vs. polyostotic) must query the treating provider before assigning Q78.1, since monostotic fibrous dysplasia does not map here. For an overview of how coding hierarchies apply across diagnostic categories, the related ICD-10 diagnostic codes article illustrates similar parent-child specificity rules.

Q78 parent code: Type 2 excludes notes

The parent category Q78 carries a Type 2 Excludes note. This is important for coding McCune-Albright syndrome cases with endocrine complications.

A Type 2 Excludes note means the excluded condition is not part of the condition represented by Q78, but both conditions can be present simultaneously. When a Type 2 Excludes note appears, it is acceptable to report both Q78.1 and the excluded code together on the same claim when both conditions are independently documented and clinically relevant.

For McCune-Albright syndrome patients with precocious puberty, hyperthyroidism, or other endocrine manifestations, coders should add the appropriate endocrine disorder code alongside Q78.1. The Q78.1 code alone does not capture the endocrine component. This multi-code approach is consistent with HIPAA-covered transaction requirements for comprehensive diagnosis reporting.

Monostotic vs. polyostotic fibrous dysplasia: coding distinction

This differential is the most common source of coding errors for fibrous dysplasia claims. The distinction matters because the two forms do not share a code.

When radiology or pathology reports describe “fibrous dysplasia” without specifying monostotic or polyostotic, the coder cannot assume Q78.1. A provider query is required. Many practices using dermatology EMR software or musculoskeletal-focused EHR systems configure condition templates that capture this distinction at the point of documentation, reducing downstream query volume.

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ICD-10 Code Q78.1: Documentation requirements

Accurate Q78.1 coding depends on what the treating provider has documented. Coders cannot assign this code based on a radiologic impression alone when the clinical note does not confirm the diagnosis. Clinical documentation compliance requirements apply equally to congenital bone disorder records.

Required documentation elements

• Confirmed diagnosis: Physician, orthopedic surgeon, or endocrinologist must state “polyostotic fibrous dysplasia” or “McCune-Albright syndrome” explicitly in the clinical note.
• Multi-site evidence: Documentation must reflect involvement of more than one bone (radiographic reports, bone survey findings, or clinical narrative confirming polyostotic presentation).
• Syndrome components (when applicable): If McCune-Albright syndrome is the diagnosis, document each active manifestation (skeletal, endocrine, dermatologic) to support additional codes beyond Q78.1.
• Active vs. historical: Q78.1 may be reported as a current condition or as a historical diagnosis affecting current management, consistent with ICD-10-CM official guideline Section I.C.

Practices using structured medical documentation workflows can embed condition-specific templates that prompt providers to document the number of affected sites, known endocrine complications, and current treatment status, ensuring every claim includes the specificity needed for Q78.1 assignment without a separate coder query.

ICD-10-PCS procedural pairings

For inpatient claims, Q78.1 as a principal or secondary diagnosis may pair with ICD-10-PCS procedure codes covering bone biopsy, curettage and bone grafting, osteotomy, or corrective fracture repair. The specific PCS code depends on the surgical approach and affected body part. Outpatient claims pair Q78.1 with relevant CPT procedure codes, which must satisfy medical necessity per payer LCD policies. Verify payer-specific policies through your clearinghouse or the AAPC Codify ICD-10-CM lookup for current crosswalk data.

Related ICD-10 codes and coding workflow for Q78.1

Q78.1 rarely appears in isolation on a claim. Understanding which secondary and additional codes apply makes a significant difference to reimbursement accuracy and audit readiness. Keeping structured patient records with linked diagnosis codes supports this workflow. Practices with patient record management tools that allow multi-code diagnosis lists at the encounter level avoid the fragmented documentation that drives claim edits.

Commonly paired additional codes

• E30.1 (Precocious puberty): Report alongside Q78.1 when McCune-Albright syndrome presents with early-onset puberty in female patients.
• E05.90 (Hyperthyroidism, unspecified): McCune-Albright syndrome is a recognised cause of non-autoimmune hyperthyroidism; add when documented.
• M84.58xA / M84.58xD (Pathological fracture in other disease): When fibrous dysplastic bone sustains a fracture, code the fracture with the appropriate 7th character for encounter type.
• Z82.61 (Family history of arthritis): May appear in the context of long-term orthopedic monitoring but does not replace an active Q78.1 diagnosis code.

Practices integrating digital intake forms into the initial patient encounter can pre-populate the condition checklist from patient history, reducing the time clinicians spend reviewing prior records before documenting the current encounter.

SNOMED CT mapping

For EHR systems using SNOMED CT, polyostotic fibrous dysplasia maps to SNOMED concept 27939004. McCune-Albright syndrome maps to SNOMED concept 33911001. When a clinical record uses SNOMED terminology and the billing system requires ICD-10-CM, the correct crosswalk landing code is Q78.1 for both. Verify current mappings through the NLM SNOMED CT browser before configuring automated crosswalk rules in your billing system.

Coding workflow for Q78.1 in practice

Getting from a clinical note to a clean Q78.1 claim involves four practical steps. Each step has a common failure point coders should watch for.

1. Confirm the qualifier: The clinical note must say “polyostotic.” If it says only “fibrous dysplasia,” issue a provider query before coding.
2. Check for syndrome components: If McCune-Albright syndrome is named, scan the note for documented endocrine and dermatologic features. Each active component supports an additional code alongside Q78.1.
3. Apply Type 2 Excludes logic: Review the Q78 parent-code excludes note. If an endocrine condition is present and separately documented, report both Q78.1 and the endocrine code.
4. Verify procedural pairing: Confirm the CPT or ICD-10-PCS code for the encounter is supported by Q78.1 under the applicable payer’s LCD or NCD. Attach supporting documentation if required.

Practices using claims management software can automate the specificity check at claims scrubbing, flagging encounters where “fibrous dysplasia” appears in the note without a Q78.1 assignment, prompting the coder before submission rather than after a denial. For the broader context of how EHR data flows into diagnostic coding, EHR integration for diagnostic coding covers the key decision points practices face when configuring these workflows.

Conclusion

Polyostotic fibrous dysplasia is a rare but consistently coded condition, and Q78.1 is the single billable code that captures it. The most frequent errors are assigning the non-specific parent Q78, failing to query when documentation says only “fibrous dysplasia,” and omitting endocrine disorder codes when McCune-Albright syndrome is the clinical picture.

Pabau’s compliance management tools help practices structure encounters so the diagnostic specificity required for clean Q78.1 claims is captured at the point of care, before a denial forces a rework cycle. To see how Pabau handles ICD-10 coding workflows from documentation through claim submission, book a demo.

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