2027 ICD-10-CM Diagnosis Code G71.12Myotonia congenita
ICD-10-CM Codes›G00–G99›G70-G73›G71
- Billable — Valid for Submission
- Chronic Condition
G71.12 is a billable ICD-10-CM diagnosis code for myotonia congenita. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 91 through 93. Coders also document this condition as acetazolamide responsive myotonia. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Myopathies.
G71.12 does not risk-adjust for Medicare Advantage under the CMS-HCC V28 model. It still risk-adjusts in the ESRD (V21) category 75 for payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
G71.12 does not risk-adjust for Medicare Advantage under the CMS-HCC V28 model, but it maps to payment categories in the other CMS models shown below.
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.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Acetazolamide responsive myotonia
- Congenital myotonia, autosomal dominant form
- Congenital myotonia, autosomal recessive form
- Myotonia congenita
- Myotonia levior
- Potassium aggravated myotonia
- Richieri Costa-da Silva syndrome
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to G71.12: its own notes plus those printed at G71 and Chapter 6. A note printed at a category, block or chapter applies to every code under it.
Applicable To
Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.
- Acetazolamide responsive myotonia congenita
- Dominant myotonia congenita [Thomsen disease]
- Myotonia levior
- Recessive myotonia congenita [Becker disease]
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.
- certain conditions originating in the perinatal period (P04-P96)
- certain infectious and parasitic diseases (A00-B99)
- complications of pregnancy, childbirth and the puerperium (O00-O9A)
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
- endocrine, nutritional and metabolic diseases (E00-E88)
- injury, poisoning and certain other consequences of external causes (S00-T88)
- neoplasms (C00-D49)
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name G71.12, its category, or a range that includes it.
Excludes2 1
These codes carry an Excludes2 note naming G71.12: its condition is not part of those codes, and both may be reported when the patient has both.
- Block M60-M63 Disorders of muscles
Code First 2
These codes say to code first a condition named in the note, and G71.12 is one of the conditions named.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Disease, diseased See Also: Syndrome;
myotonia congenita G71.12
Thomsen G71.12
Thomsen disease G71.12
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Myotonia Congenita
inherited myotonic disorders with early childhood onset myotonia. muscular hypertrophy is common and myotonia may impair ambulation and other movements. it is classified as thomsen (autosomal dominant) or becker (autosomal recessive) generalized myotonia mainly based on the inheritance pattern. becker type is also clinically more severe. an autosomal dominant variant with milder symptoms and later onset is known as myotonia levior. mutations in the voltage-dependent skeletal muscle chloride channel are associated with the disorders.
Patient EducationClinical
Neuromuscular Disorders
Neuromuscular disorders affect your neuromuscular system. They can cause problems with:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert G71.12 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About G71.12Overview
What is the ICD-10 code for myotonia congenita?
The ICD-10-CM code for myotonia congenita is G71.12 (sometimes written as G7112). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is G71.12 (Myotonic disorders) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report myotonia congenita on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does G71.12 group to?
When myotonia congenita is the principal diagnosis on an inpatient stay, it groups to MS-DRG 91, 92, 93, with relative weights from 0.7783 to 1.7050 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of G71.12?
Under the General Equivalence Mappings, myotonia congenita converts to ICD-9-CM 359.22 (myotonia congenita). The mapping is a direct match.
Does G71.12 risk-adjust for Medicare Advantage payment?
Not for Medicare Advantage: G71.12 maps to no category in the CMS-HCC V28 model. It still risk-adjusts in the ESRD (V21) category 75 (Polyneuropathy).
