Short answer · Medically reviewed summary · Last updated: 2026-05-08
Hyperekplexia, also known as startle disease, is classified under the ICD-10 code G25.89 (Other specified extrapyramidal and movement disorders) and the ICD-9 code 333.99 (Other extrapyramidal diseases and abnormal movement disorders). These codes are used by medical providers for billing and administrative purposes, though they do not capture the specific genetic nuances of this rare neurological condition. What is the clinical classification of Hyperekplexia? Hyperekplexia is a rare hereditary neurological disorder characterized by an excessive startle response to unexpected auditory, tactile, or visual stimuli.
ICD10 code of Hyperekplexia and ICD9 code
ICD-10 and ICD-9 codes for Hyperekplexia, with classification details for clinicians, coders and patients.
Hyperekplexia, also known as startle disease, is classified under the ICD-10 code G25.89 (Other specified extrapyramidal and movement disorders) and the ICD-9 code 333.99 (Other extrapyramidal diseases and abnormal movement disorders). These codes are used by medical providers for billing and administrative purposes, though they do not capture the specific genetic nuances of this rare neurological condition.
What is the clinical classification of Hyperekplexia?
Hyperekplexia is a rare hereditary neurological disorder characterized by an excessive startle response to unexpected auditory, tactile, or visual stimuli. Because it is a rare condition, it does not have a unique, dedicated ICD code and instead falls under broader neurological categories. Understanding that Hyperekplexia is often misdiagnosed as epilepsy is vital for patients seeking appropriate care, as the two conditions require vastly different treatment protocols.
Is Hyperekplexia hereditary?
Yes, Hyperekplexia is primarily a genetic disorder. It is most commonly caused by mutations in the GLRA1 gene, which encodes the alpha-1 subunit of the glycine receptor. The condition can be inherited in either an autosomal dominant or an autosomal recessive pattern. Genetic counseling is strongly recommended for families affected by Hyperekplexia to understand the transmission risks and the specific genetic profile involved.
What are the primary symptoms and diagnostic markers?
Clinical presentation of Hyperekplexia typically includes a life-long history of exaggerated startle reflexes and periodic muscle stiffness (hypertonia). Key clinical features include:
- Exaggerated startle response that does not habituate with repeated stimuli.
- Neonatal hypertonia, which often leads to an initial misdiagnosis of spastic cerebral palsy.
- "Head retraction reflex" in infants, where a tap on the nose causes the infant to arch their back and pull their head back.
- Nocturnal myoclonus (jerking movements during sleep).
Next steps
- Consult a neurologist specializing in movement disorders to confirm a Hyperekplexia diagnosis through genetic testing.
- Join our community of 56 members on DiseaseMaps.org to share experiences and coping strategies for managing the startle response.
- Discuss the use of benzodiazepines, such as clonazepam, with your physician, as this is the current gold-standard treatment for symptoms.
Medical disclaimer: This information is for educational purposes only and does not constitute medical advice, diagnosis, or treatment; always seek the advice of a qualified healthcare provider with any questions regarding a medical condition.
References
- Orphanet: Hyperekplexia (ORPHA:415)
- NIH Genetic and Rare Diseases (GARD) Information Center: Hyperekplexia
- OMIM (Online Mendelian Inheritance in Man): Hyperekplexia 1; HKPX1 (#149400)
- PubMed: Clinical and genetic overview of hereditary hyperekplexia
