myelitis

DEFINITION of myelitis

myelitis is inflammation of the spinal cord, a condition that damages myelin and/or axons and leads to varying degrees of motor, sensory, and autonomic impairment. It is distinguished from encephalitis (inflammation of the brain) and meningitis (inflammation of the meninges), though overlapping syndromes like meningoencephalitis or encephalomyelitis can occur. The pathological mechanism involves immune-mediated attack (autoimmune, postinfectious) or direct microbial invasion (viral, bacterial, fungal, parasitic) causing edema, demyelination, and neuronal injury. Myelitis can be acute or subacute in onset and is classified as either idiopathic (no identifiable cause), postinfectious (e.g., after COVID-19, EBV, Mycoplasma), or disease‑associated (e.g., multiple sclerosis, neuromyelitis optica spectrum disorder (NMOSD), sarcoidosis). Clinically relevant subtypes encountered in coding include transverse myelitis (complete or partial cord involvement across a horizontal level, often with a sensory level; ICD‑10‑CM G37.3 for demyelinating acute transverse myelitis, or G04.89 for other specified myelitis), polio (viral myelitis of anterior horn cells; A80.9), and parainfectious myelitis (G04.82). Unlike multiple sclerosis (where myelitis is typically one of many relapsing episodes with dissemination in time and space), isolated myelitis may remain a monophasic illness or be the first attack of a systemic disorder.

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ETYMOLOGY of myelitis

greek

Component	Origin	Meaning
myel-	borrowed directly from Neo-Latin myelitis	from Greek myelós (“marrow, spinal cord”)
-itis	Greek μυελός (myelós) (pronounced “moo-eh-LOS”)	“marrow” (later specifically “spinal cord” or “bone marrow” in medical contexts)
-ic	Greek -ῖτις (-îtis) (pronounced “EE-tis”)	Noun-forming suffix — “inflammation” (originally feminine adjective meaning “pertaining to,” later used substantively for inflammatory diseases)

The word entered English in the 1820s as myelitis (noun), borrowed directly from Neo-Latin myelitis, from Greek myelós (“marrow, spinal cord”) + -îtis (“inflammation”). The term originally referred to inflammation of bone marrow but was quickly restricted to the spinal cord to avoid confusion with osteomyelitis. The root myel- (“marrow/core”) connects myelitis to the entire -MYEL FAMILY]]: myelin (literally “little marrow” → the insulating sheath of nerves), myelocyte (marrow cell → a precursor in granulopoiesis), and myeloma (marrow tumor). The suffix -itis is one of the most productive in medicine, appearing in appendicitis, arthritis, meningitis, pancreatitis, and tonsillitis.

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🔀 ALIASES / ALTERNATE TERMS

• Myelitic (adjective form — “myelitic lesions,” “myelitic pain,” “myelitic gait disturbance”)
• Inflammation of the spinal cord (plain‑language lay term)
• Partial myelitis (incomplete cord involvement; often presents with asymmetric or unilateral symptoms)
• Focal myelitis]] (localized inflammation confined to one segment, e.g., cervical myelitis)
• Disseminated myelitis]] (multifocal cord inflammation, may mimic multiple sclerosis; coded under G04.89)
• Necrotizing myelitis (severe form with tissue necrosis; seen in paraneoplastic syndromes or NMOSD; often requires immunotherapy)
• Postinfectious myelitis]] (immune‑mediated onset 1-4 weeks after viral/bacterial infection; coded G04.82 or G04.89)
• Parainfectious myelitis (clinically synonymous with postinfectious; same coding)
• Idiopathic myelitis (no cause identified after full workup; coded G04.91 if unspecified, or G04.82 for other myelitis)
• Transverse myelitis (complete horizontal cord involvement with bilateral signs and a sensory level; classic acute/subacute presentation; demyelinating form = G37.3, other/idiopathic = G04.89)
• Longitudinally extensive transverse myelitis (LETM) (inflammation spanning ≥3 vertebral segments on MRI; strongly associated with AQP4‑IgG+ NMOSD; coded G36.0 - neuromyelitis optica)

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🔗 RELATED TERMS

• Osteomyelitis — the opposite (or rather, different anatomic site) of myelitis; inflammation of bone marrow (not spinal cord). Confusion arises from shared root myel-; note that “myelitis” almost always refers to spinal cord in neurology, while “osteomyelitis” refers to bone.
• Myelopathy — shares the myel- root; any disease of the spinal cord regardless of etiology (degenerative, vascular, compressive, inflammatory). Myelitis is a specific inflammatory subtype of myelopathy. Non‑inflammatory myelopathies (e.g., cervical spondylotic myelopathy) are not coded as myelitis.
• Encephalomyelitis — closely related clinical entity where inflammation involves both brain and spinal cord; ICD‑10‑CM G04.00 (acute disseminated encephalomyelitis, ADEM) or G04.01 (postinfectious ADEM). Overlap: myelitis with encephalopathy suggests this diagnosis.
• Neuromyelitis optica spectrum disorder (NMOSD) — complex syndrome that classically pairs optic neuritis with longitudinally extensive transverse myelitis; mediated by aquaporin‑4 antibodies; coded G36.0. Co‑diagnosed with myelitis in >50% of cases.
• Demyelination — mechanism term; the immune‑mediated loss of myelin sheaths, a key pathological process in many myelitis subtypes (especially those associated with multiple sclerosis or NMOSD).
• Trophic — adjective form of mechanism; “trophic support” refers to neurotrophic factors that maintain neuronal health; loss of such support is not a primary driver of myelitis (unlike atrophy).
• Apoptosis — cellular mechanism term; programmed cell death that may occur in neurons and oligodendrocytes during myelitis, contributing to permanent disability.
• Acute disseminated encephalomyelitis (ADEM) — disease entity using this term; monophasic, postinfectious inflammatory demyelination of brain and spinal cord; ICD‑10‑CM G04.00 (ADEM) or G04.01 (postinfectious ADEM).
• Multiple sclerosis (MS) — disease entity that includes myelitis as a common relapsing manifestation; coded under G35.A. Distinction: MS requires dissemination in time and space; isolated myelitis does not fulfill MS criteria unless additional lesions appear.
• Viral myelitis — e.g., enterovirus D68‑associated acute flaccid myelitis (AFM); coded G04.82 with additional B97.1- for enterovirus; poliomyelitis (A80.9) is a historic but distinct viral anterior horn cell myelitis.
• Herpes zoster myelitis — segmental myelitis following reactivation of varicella‑zoster virus; coded B02.23 (zoster myelitis) as a primary code plus G04.82 as needed.
• Paraneoplastic myelitis — autoimmune myelitis associated with underlying malignancy (e.g., small cell lung cancer with anti‑amphiphysin antibodies); code malignancy first, then G13.0 (paraneoplastic neuromyopathy) or G04.89.
• Magnetic resonance imaging (MRI) of spine — primary diagnostic tool for evaluating myelitis; detects T2 hyperintensity, cord swelling, contrast enhancement; CPT codes 72141 (without contrast), 72146 (with contrast).

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CODING CORNER

🏥 ICD-10-CM CODES

Myelitis (G04.9 - G04.8 Family - Site and Etiology Required When Known)

Code	Description
G04.91	Myelitis, unspecified (use only when workup incomplete; avoid for inpatient profee if MRI or CSF results exist)
G04.82	Other myelitis (specified non‑infectious, postinfectious, idiopathic with sufficient documentation)
G04.89	Other specified encephalitis, myelitis and encephalomyelitis (includes focal myelitis, disseminated myelitis, chronic myelitis)
G04.00	Acute disseminated encephalomyelitis (ADEM) - includes encephalomyelitis with spinal cord involvement
G04.01	Postinfectious acute disseminated encephalomyelitis (postinfectious ADEM)
G37.3	Acute transverse myelitis in demyelinating disease of central nervous system (use for MS‑associated or isolated demyelinating transverse myelitis)
G36.0	Neuromyelitis optica (Devic’s disease) - includes longitudinally extensive transverse myelitis as core feature
A80.9	Acute poliomyelitis, unspecified (viral anterior horn cell myelitis; reportable disease)
B02.23	Zoster myelitis (herpes zoster with myelitis) - use as principal diagnosis if myelitis is the primary manifestation
G13.0	Paraneoplastic neuromyopathy and neuropathy (includes paraneoplastic myelitis; code neoplasm first)

Infectious Myelitis (Specific Organism Codes) - Use Additional Code for Causative Agent

Code	Description
G04.81	Other encephalitis and encephalomyelitis (used for infectious myelitis when organism specified, e.g., syphilitic, Lyme)
A52.11	Syphilitic myelitis (tabes dorsalis with cord involvement) - confirm with CSF VDRL
A69.22	Lyme disease myelitis (neuroborreliosis with myelitis) - use additional code for late neurological manifestations
B58.01	Toxoplasma myelitis (common in immunocompromised, e.g., HIV) - code HIV status first if applicable
B37.4	Candidal myelitis (rare, usually in disseminated candidiasis)

Acute Flaccid Myelitis (AFM) - Specific Enterovirus‑Associated Subtype

Code	Description
G04.82	Other myelitis (use with additional code B97.19 for other enterovirus as cause)
B97.11	Enterovirus D68 as the cause of diseases classified elsewhere - report together with G04.82

Myelitis in Systemic Autoimmune Disease - Code Underlying Disease First

Code	Description
M32.19	Systemic lupus erythematosus with other organ or system involvement (including myelitis) - code SLE first, then G04.82
M35.02	Sjögren’s syndrome with myelitis
D86.89	Sarcoidosis with other specified manifestations (neurosarcoidosis with myelitis)
M30.3	Kawasaki disease with neurologic involvement (rare myelitis)

Skin / Integumentary Form - Not applicable; myelitis is not a cutaneous condition

Code	Description
—	No direct skin codes for myelitis; secondary pressure ulcers from paralysis use L89.- series with site specifiers

Genitourinary / Autonomic Complications - Myelitis‑Associated Neurogenic Bladder

Code	Description
N31.9	Neuromuscular dysfunction of bladder, unspecified (due to myelitis) - code G04.82 as principal if bladder dysfunction is the presenting symptom
N31.0	Uninhibited neuropathic bladder, not elsewhere classified
N31.1	Reflex neuropathic bladder
N31.2	Flaccid neuropathic bladder

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🔧 COMMON CPT CODES (Myelitis‑Related Diagnosis & Treatment)

CPT Code	Description
72141	Magnetic resonance imaging (MRI) of spinal canal, without contrast material - cervical (initial screening for myelitis)
72142	MRI of spinal canal, without contrast followed by contrast - cervical (evaluate blood‑brain barrier disruption)
72146	MRI of spinal canal, without contrast - thoracic (common for transverse myelitis)
72147	MRI of spinal canal, without contrast followed by contrast - thoracic
72148	MRI of spinal canal, without contrast - lumbar (less common in myelitis unless conus involvement)
72149	MRI of spinal canal, without contrast followed by contrast - lumbar
62270	Spinal puncture, lumbar, diagnostic (CSF analysis for oligoclonal bands, IgG index, AQP4 antibodies, infection studies)
95907	Nerve conduction studies, 1-2 studies (to assess for peripheral nerve overlap, rule out Guillain‑Barré)
95869	Needle electromyography (EMG) of thoracic paraspinal muscles (detects denervation from anterior horn cell involvement)
95870	Needle EMG of 1-2 muscles of lower extremity (evaluate extent of motor unit loss)
95938	Somatosensory evoked potentials (SSEPs) - lower extremities (assess dorsal column function in myelitis)
95939	SSEPs - upper and lower limbs, combined
97110	Therapeutic procedure, 15 min - therapeutic exercise to develop strength and endurance (post‑myelitis rehabilitation)
97535	Self‑care/home management training, 15 min - for neurogenic bowel/bladder management
97530	Therapeutic activities, direct patient contact, 15 min - balance and gait retraining

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⚠️ Coding Note: For inpatient profee coding, site specificity is critical: specify the cord level (cervical, thoracic, lumbar, or conus) in the documentation. The ICD‑10‑CM codes for myelitis (G04.82, G04.89, G37.3) do not have laterality or site sub‑classifications, but accurate localization affects medical necessity for MRI (CPT 72141 vs 72146). Sequencing logic: If the myelitis is due to a known underlying condition (e.g., systemic lupus, NMOSD, sarcoidosis, herpes zoster), code the underlying disease first as principal diagnosis, then G04.82 or the specific myelitis code as secondary. Exception: acute flaccid myelitis due to enterovirus - code G04.82 principal, then B97.11 for the organism. Undercoding alert: Many inpatient claims miss the specific code G04.82 for “other myelitis” and default to G04.91 (unspecified). Documentation phrases like “idiopathic transverse myelitis,” “postinfectious myelitis,” “longitudinally extensive myelitis” should trigger a query for specificity and avoid unspecified code. Payer considerations: For neuromyelitis optica‑associated myelitis, prior authorization for eculizumab or rituximab often requires the specific code G36.0 and demonstration of AQP4‑IgG positivity. Type/subtype specificity: Acute transverse myelitis due to multiple sclerosis requires G37.3; if MS is not yet diagnosed but suspected, code G04.82 and add G35.A only after McDonald criteria are met. For genetic testing (e**.g., to rule out hereditary myelopathies**), confirm that the myelitis is truly inflammatory - do not order genetic panels under a myelitis code unless demyelinating etiology is excluded.

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DERIVATIONS of myelitis

TABLE definition AS Definition
FROM #medterm 
WHERE length(filter(roots, (word) => econtains([[myelitis]].roots, word))) > 0 AND file.name != [[myelitis]].file.name
SORT file.name ASC

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Query functionality

TABLE definition AS Definition
FROM #medterm 
WHERE length(filter(definition, (word) => econtains([[myelitis]].definition, word))) > 0 AND file.name != [[myelitis]].file.name

Med roots dictionary Appendix A Prefixes Appendix B Combining Forms Appendix C Suffixes Appendix D Suffix forms