2026 ICD-10-CM Diagnosis Code G71.12Myotonia congenita

ICD-10-CM Codes›G00–G99›G70-G73›G71

ICD-10-CM G71.12
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

G71.12 is a billable ICD-10-CM diagnosis code for myotonia congenita. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). Coders also document this condition as acetazolamide responsive myotonia. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Myopathies.

Code Identity

ICD-10-CM Code
G71.12
Billable Status
Yes — Valid for Submission
Code Describes
Myotonia congenita
Short Description
Myotonia congenita
Same as the full description in the CMS dataset.
Parent Code
G71.1
Myotonic disorders

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG70-G73Diseases of myoneural junction and muscle
CategoryG71Primary disorders of muscles
This CodeG71.12Myotonia congenita

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

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Acetazolamide responsive myotonia congenita
  • Dominant myotonia congenita Thomsen disease
  • Myotonia levior
  • Recessive myotonia congenita Becker disease

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Becker's
      • disease
        • myotonia congenita, recessive form
    • Disease, diseased
      • Becker
        • myotonia congenita
    • Disease, diseased
      • Thomsen
    • Myotonia(acquisita) (intermittens)
      • congenita (acetazolamide responsive) (dominant) (recessive)
    • Myotonia(acquisita) (intermittens)
      • levior
    • Thomsen disease

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NVS018
Myopathies
Default principal diagnosis: inpatient Yes · outpatient Yes

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.

  • Myotonia

    prolonged failure of muscle relaxation after contraction. this may occur after voluntary contractions, muscle percussion, or electrical stimulation of the muscle. myotonia is a characteristic feature of myotonic disorders.

  • Myotonia Congenita

    a genetic congenital neuromuscular disorder affecting the skeletal muscles. it is caused by mutations in the chloride channel gene (clcn1 gene). it is characterized by muscle stiffness, hypertrophy, pain, and cramping.

  • Paramyotonia Congenita without Cold Paralysis

    an autosomal dominant inherited non-dystrophic myotonia caused by mutations of the scn4a gene. it is characterized by muscle stiffness, which is increased by exposure to cold but does not change to flaccid paralysis with intense cooling.

  • Paramyotonia Congenita|PMC|Paramyotonia Congenita of von Eulenburg

    an autosomal dominant inherited non-dystrophic myotonia caused by mutations of the scn4a gene, resulting in sodium muscle channelopathy. it is characterized by muscle stiffness, which is increased by exposure to cold or activity, and usually eases when the patient warms up through physical activity.

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.

ICD-9-CM
359.22 Myotonia congenita
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About G71.12Overview

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, 2025 through September 30, 2026.

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.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.