Skip to content
HCC Buddy home

E88.42 ICD-10-CM Code: MERRF syndrome

E88.42 is not a CMS-HCC payment code. MEAT criteria · RAF Calculator · free HCC coding tools

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupE88.42

FY 2026 Apr update / Endocrine, nutritional and metabolic diseases (E00-E89) / Metabolic disorders (E70-E88)

E88.42

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

MERRF syndrome

MERRF syndrome is a rare inherited mitochondrial disorder characterized by myoclonic seizures, ragged-red muscle fibers, and progressive neurological decline.

Buddy the Bee presenting code insight

Buddy Insight

MERRF (Myoclonic Epilepsy associated with Ragged Red Fibers) syndrome is a mitochondrial disorder characterized by myoclonus, epilepsy, ataxia, and progressive muscle weakness.

OverviewRisk ModelsCode BookDocumentationAuditNotesEdition comparison

CMS-HCC V28

N/A

—

Not mapped

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

Context needed

HCC 028

Coefficient needs member context

ESRD/PACE

Context needed

HCC 23

Coefficient needs member context

RXHCC

HCC 43

Code-level coefficient reference

Code Book Path

Official
E88Other and unspecified metabolic disordersE88.4Mitochondrial metabolism disordersE88.42MERRF syndrome

Inclusion Terms

Official
  • Myoclonic epilepsy associated with ragged-red fibers

Excludes 2

Official
  • Ehlers-Danlos syndromes (Q79.6-)Inherited from E70-E88

Related Codes

Official
E88.40Mitochondrial metabolism disorder, unspecifiedE88.41MELAS syndromeE88.43Disorders of mitochondrial tRNA synthetasesE88.49Other mitochondrial metabolism disorders

Includes

Official

No Includes notes are included in this display for E88.42. Check the code and parent instructions in the Code Book.

Excludes 1

Official
  • transitory endocrine and metabolic disorders specific to newborn (P70-P74)Inherited from E00-E89, E70-E88, E88, E88.4
  • androgen insensitivity syndrome (E34.5-)Inherited from E00-E89, E70-E88, E88, E88.4
  • congenital adrenal hyperplasia (E25.0)Inherited from E00-E89, E70-E88, E88, E88.4
  • hemolytic anemias attributable to enzyme disorders (D55.-)Inherited from E00-E89, E70-E88, E88, E88.4
  • Marfan syndrome (Q87.4-)Inherited from E00-E89, E70-E88, E88, E88.4
  • 5-alpha-reductase deficiency (E29.1)Inherited from E00-E89, E70-E88, E88, E88.4
  • histiocytosis X (chronic) (C96.6)Inherited from E00-E89, E70-E88, E88, E88.4
  • disorders of pyruvate metabolism (E74.4)Inherited from E00-E89, E70-E88, E88, E88.4
  • Kearns-Sayre syndrome (H49.81)Inherited from E00-E89, E70-E88, E88, E88.4
  • Leber's disease (H47.22)Inherited from E00-E89, E70-E88, E88, E88.4
  • Leigh's encephalopathy (G31.82)Inherited from E00-E89, E70-E88, E88, E88.4
  • Mitochondrial myopathy, NEC (G71.3)Inherited from E00-E89, E70-E88, E88, E88.4
  • Reye's syndrome (G93.7)Inherited from E00-E89, E70-E88, E88, E88.4

Code First

Official

No Code First sequencing instructions are included in this display for E88.42. Check the code and parent instructions in the Code Book.

Use Additional

Official
  • codes for associated conditionsInherited from E88

Code Also

Official
  • progressive myoclonic epilepsy (G40.3-)

Buddy Documentation Tip

HCC Buddy guidance
Confirmed MERRF diagnosis (clinical criteria plus genetic testing, typically m.8344A>G mutation)
Documentation of myoclonic epilepsy as a key feature
Muscle biopsy showing ragged red fibers (if performed)
Genetic testing results confirming mitochondrial DNA mutation

MEAT Support

HCC Buddy guidance
Confirmed MERRF diagnosis (clinical criteria plus genetic testing, typically m.8344A>G mutation)
Documentation of myoclonic epilepsy as a key feature
Muscle biopsy showing ragged red fibers (if performed)
Genetic testing results confirming mitochondrial DNA mutation

Audit Caution

HCC Buddy guidance
Coding only the epilepsy or myoclonus without the underlying MERRF syndrome
Confusing MERRF with MELAS — different mutations and clinical presentations
Using the unspecified mitochondrial code when MERRF is documented
Not recognizing that ragged red fibers on muscle biopsy support MERRF diagnosis

Common Mistakes

HCC Buddy guidance
E88.41 — MELAS syndrome: different mitochondrial syndrome with stroke-like episodes as primary feature
E88.40 — Mitochondrial metabolism disorder, unspecified: less specific; use E88.42 when MERRF is confirmed
G40.401 — Other generalized epilepsy, not intractable, with status epilepticus: epilepsy without the mitochondrial context
G25.3 — Myoclonus: symptom code that does not capture the underlying mitochondrial disorder

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is E88.42 an HCC code?

E88.42 has no mapping under the current CMS-HCC V28 community payment model. E88.42 has a separate mapping under the CMS-HCC ESRD model (HCC 23 (Other Significant Endocrine and Metabolic Disorders)) and the Part D RxHCC model (HCC 43 (Pituitary, Adrenal Gland, and Other Endocrine and Metabolic Disorders)); the applicable result needs member context. E88.42 also appears in the HHS-HCC commercial risk model (HCC 028 (HHS-HCC 028 child, RAF varies by metal level)), where the result depends on member context and is not a Medicare Advantage payment mapping.

Code
E88.42
Description
MERRF syndrome
HCC (V28)
No CMS-HCC V28 mapping
RAF reference coefficient
—
Billable
Yes
Payment year
2026

HCC Category Mapping

RxHCCHCC 43, Pituitary, Adrenal Gland, and Other Endocrine and Metabolic Disorders
Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work E88.42 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for E88.42

For E88.42, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

  • MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
  • EEvaluate: test results, medication response, or physical findings reviewed by the provider
  • AAssess: explicit mention in the assessment or plan with acknowledgment of status
  • TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Coder workflow notes

Get the V28 mapping + MEAT cheat sheet

One printable reference: check representative V28 mappings and the documentation reminders your note needs. Free, no card.

Free PDF. No card. Unsubscribe anytime.

What This Code Means

E88.42 is the ICD-10-CM diagnosis code for merrf syndrome. MERRF syndrome is a rare inherited mitochondrial disorder characterized by myoclonic seizures, ragged-red muscle fibers, and progressive neurological decline. E88.42 sits in the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89), within the section covering metabolic disorders (e70-e88).

E88.42 has no mapping under the current CMS-HCC V28 community payment model. E88.42 has a separate mapping under the CMS-HCC ESRD model (HCC 23 (Other Significant Endocrine and Metabolic Disorders)) and the Part D RxHCC model (HCC 43 (Pituitary, Adrenal Gland, and Other Endocrine and Metabolic Disorders)); the applicable result needs member context. E88.42 also appears in the HHS-HCC commercial risk model (HCC 028 (HHS-HCC 028 child, RAF varies by metal level)), where the result depends on member context and is not a Medicare Advantage payment mapping. Do not assign V28 risk adjustment value from this page; verify the applicable model and payment year before using this code for risk adjustment.

MERRF stands for Myoclonic Epilepsy with Ragged-Red Fibers; document the specific neurological manifestations present.

HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for E88.42 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •MERRF stands for Myoclonic Epilepsy with Ragged-Red Fibers; document the specific neurological manifestations present
  • •This is a specific mitochondrial disorder code and should be used when MERRF is confirmed rather than the unspecified E88.40

Clinical Significance

MERRF (Myoclonic Epilepsy associated with Ragged Red Fibers) syndrome is a mitochondrial disorder characterized by myoclonus, epilepsy, ataxia, and progressive muscle weakness. The 'ragged red fibers' on muscle biopsy are pathognomonic. This rare condition requires specialized neurological and metabolic management.

Documentation Requirements

  • ✓Confirmed MERRF diagnosis (clinical criteria plus genetic testing, typically m.8344A>G mutation)
  • ✓Documentation of myoclonic epilepsy as a key feature
  • ✓Muscle biopsy showing ragged red fibers (if performed)
  • ✓Genetic testing results confirming mitochondrial DNA mutation
  • ✓Neurological assessment including seizure characterization
  • ✓Multi-system evaluation (cardiac, hearing, endocrine)
  • ✓Current treatment regimen (antiepileptic medications, metabolic support)

Code Also

  • progressive myoclonic epilepsy (G40.3-)

Commonly Confused Codes

  • •E88.41: MELAS syndrome: different mitochondrial syndrome with stroke-like episodes as primary feature
  • •E88.40: Mitochondrial metabolism disorder, unspecified: less specific; use E88.42 when MERRF is confirmed
  • •G40.401: Other generalized epilepsy, not intractable, with status epilepticus: epilepsy without the mitochondrial context
  • •G25.3: Myoclonus: symptom code that does not capture the underlying mitochondrial disorder

Child Codes

E88.40Mitochondrial metabolism disorder, unspecified
E88.41MELAS syndrome
E88.42MERRF syndrome
E88.43Disorders of mitochondrial tRNA synthetases
E88.49Other mitochondrial metabolism disorders

Code Hierarchy

└E88Other and unspecified metabolic disorders└E88.4Mitochondrial metabolism disorders└E88.42MERRF syndrome
└E88.42MERRF syndrome

Also searched as

  • E88 42
  • E8842

Work E88.42 in HCC Buddy

Open E88.42 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

Open in Code BookOpen in EncoderStart Pro