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Chapter 6: Diseases of the nervous system (G00–G99)

Diseases of the brain, spinal cord and nerves: migraine and other headache disorders, epilepsy, Parkinson's disease, Alzheimer's disease, multiple sclerosis, sleep disorders and nerve disorders.

Chapter 6 spans codes G00–G99 in the FY2027 ICD-10-CM tabular list. This guide explains 26 of its most common codes — select a code for its official description, a plain-English explanation and a note on when the code is used.

ICD-10 Chapter 6: Nervous System — illustrative image

Codes in this chapter

CodeOfficial descriptionIn plain words
G20.A1Parkinson's disease without dyskinesia, without mention of fluctuationsParkinson's disease is a progressive condition in which loss of dopamine-producing brain cells causes tremor, stiffness and slowness.
G25.0Essential tremorEssential tremor is a common involuntary shaking, usually of the hands, that worsens with movement and is not Parkinson's disease.
G25.81Restless legs syndromeRestless legs syndrome causes an urge to move the legs, usually in the evening, with uncomfortable sensations relieved by movement.
G30.9Alzheimer's disease, unspecifiedAlzheimer's disease is the most common cause of dementia, with progressive loss of memory and thinking skills.
G31.84Mild cognitive impairment of uncertain or unknown etiologyMild cognitive impairment means noticeable memory or thinking problems that are greater than expected for age but not dementia.
G40.909Epilepsy, unspecified, not intractable, without status epilepticusEpilepsy is a tendency to recurrent seizures caused by abnormal electrical activity in the brain.
G43.009Migraine without aura, not intractable, without status migrainosusMigraine without aura is a recurring headache disorder with moderate-to-severe throbbing headache, nausea and light sensitivity.
G43.109Migraine with aura, not intractable, without status migrainosusMigraine with aura includes warning symptoms such as flashing lights or zigzag lines before or during the headache.
G43.709Chronic migraine without aura, not intractable, without status migrainosusChronic migraine means headache on 15 or more days a month for over three months, with migraine features on at least 8 days.
G43.909Migraine, unspecified, not intractable, without status migrainosusMigraine is a recurring headache disorder, often one-sided and throbbing, with nausea and sensitivity to light and sound.
G44.209Tension-type headache, unspecified, not intractableTension-type headache is a mild-to-moderate, band-like headache on both sides of the head, the most common headache type.
G45.9Transient cerebral ischemic attack, unspecifiedA transient ischaemic attack (TIA, 'mini-stroke') is a brief interruption of blood flow to the brain whose symptoms resolve within 24 hours.
G47.00Insomnia, unspecifiedInsomnia is difficulty falling asleep, staying asleep, or waking too early, affecting daytime function.
G47.33Obstructive sleep apnea (adult) (pediatric)Obstructive sleep apnoea is repeated collapse of the upper airway during sleep, causing pauses in breathing and snoring.
G50.0Trigeminal neuralgiaTrigeminal neuralgia causes brief, electric-shock-like pains in the face, triggered by touch, chewing or cold air.
G51.0Bell's palsyBell's palsy is sudden weakness or paralysis of one side of the face caused by inflammation of the facial nerve.
G56.01Carpal tunnel syndrome, right upper limbCarpal tunnel syndrome is compression of the median nerve at the right wrist, causing hand numbness, tingling and weakness.
G56.02Carpal tunnel syndrome, left upper limbCarpal tunnel syndrome is compression of the median nerve at the left wrist, causing hand numbness, tingling and weakness.
G56.03Carpal tunnel syndrome, bilateral upper limbsCarpal tunnel syndrome affecting both wrists: compression of the median nerves causing numbness and tingling in both hands.
G60.9Hereditary and idiopathic neuropathy, unspecifiedNeuropathy affecting nerves throughout the body from inherited or unknown causes, often causing numbness in the feet and hands.
G62.9Polyneuropathy, unspecifiedPolyneuropathy is damage to many peripheral nerves, usually starting with numbness, tingling or pain in the feet.
G70.00Myasthenia gravis without (acute) exacerbationMyasthenia gravis is an autoimmune condition causing fluctuating muscle weakness that worsens with activity; here without an acute flare.
G80.9Cerebral palsy, unspecifiedCerebral palsy is a group of lifelong conditions affecting movement and posture from early brain injury or development.
G89.29Other chronic painChronic pain in a site other than the back that persists beyond normal healing time.
G89.4Chronic pain syndromeChronic pain syndrome is persistent pain associated with significant distress, disability or psychosocial factors.
G93.40Encephalopathy, unspecifiedEncephalopathy is a disturbance of brain function causing confusion or reduced alertness; the cause is not specified here.

This guide explains ICD-10-CM codes in plain language for patients, students and other readers. It is educational information only — not coding, billing or medical advice. The code recorded for any real encounter is assigned from the full clinical documentation by the treating team and qualified coders, and only they can decide which code fits a specific case.

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