Encephalopathy is a generalized alteration in brain function caused by an underlying systemic condition that is usually reversible. It is acute or subacute in onset and resolves when the underlying cause is treated. Common causes include infection, organ failure, drugs/toxins. Specific types include toxic, metabolic, septic encephalopathies. Accurately diagnosing encephalopathy is important for documenting severity of illness and determining principal diagnosis. While altered mental status is non-specific, encephalopathy identifies toxic/metabolic brain dysfunction. Distinguishing encephalopathy from dementia or delirium relies on determining if mental status changes are due to acute/reversible toxic or metabolic factors.

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Clinical Definition: While there are no official or specific textbook definitions, encephalopathy can be
accurately described as a generalized alteration in all aspects of brain function (communication,
memory, speech, orientation, behavior) due to a systemic underlying cause that is usually reversible. It
is typically acute (or subacute) in onset and resolves when the underlying cause is corrected.
Common causes of encephalopathy include fever, infection, dehydration, electrolyte imbalance,
acidosis, organ failure, sepsis, hypoxia, drugs, poisons or toxins.
Specific Types of Encephalopathy
Toxic encephalopathy (349.82) generally refers to the effects of drugs, toxins, poisons and medications;
but physicians may use this term clinically to refer to encephalopathy caused by fever, sepsis, or other
“toxic” conditions.
Metabolic (348.31) is intended to describe encephalopathy due to such things as fever, dehydration,
electrolyte imbalance, acidosis, hypoxia, infection and organ failure.
Toxic-metabolic encephalopathy (349.82) suggests a combination of toxic and metabolic factors and
is the same code as toxic encephalopathy.
Septic encephalopathy is a clinical term that expresses brain dysfunction as a manifestation of severe
sepsis, and is also coded 348.31. Hepatic encephalopathy is coded as 572.2 (an MCC).
Untreated uremia causes encephalopathy before it progresses to uremic coma. Do not confuse with
acute dialysis-associated encephalopathy which is classified as delirium.
Hypoxic encephalopathy codes to 348.1 (a CC), and codes for hypoxic ischemic encephalopathy (HIE)
apply only to neonates.
I-10: No significant changes. Toxic encephalopathy (G92), metabolic or septic (G93.41),
encephalopathy, NEC (G93.49), or unspecified (G93.40).
Documentation Issues: Many patients are admitted to the hospital who have, as one of their medical
problems, an altered mental status. Frequently this is the principal reason families bring them to the
office or hospital, and expect them to be admitted.
Most inpatients with an acutely altered mental status actually have “encephalopathy” causing it and
should be diagnosed as such since “altered mental status “is a non-specific Chapter 16 symptom
(780.97) which cannot be assigned whenever a more specific related diagnosis is documented.
Sometimes “altered mental status” tends to be over-diagnosed or not fully supported by the entire
medical record – for example, nursing notes that do not confirm altered mental status or conflicting

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physician documentation. In such cases, a query for clarification is appropriate, citing the conflicts in
the record.
Recognition of encephalopathy is crucial for accurate documentation of the severity of illness of
hospitalized patients. For many admissions, the principal reason for admission is actually the altered
mental status due to underlying encephalopathy. In these cases, the encephalopathy can be coded as the
PDX if it meets the definition of a principal diagnosis. For example, often patients are admitted with
encephalopathy due to UTI.
As a co-morbid secondary diagnosis, the presence of encephalopathy of almost any type (toxic, septic,
metabolic, uremic, hepatic, unspecified) qualified as an MCC. Anoxic, alcoholic and hypertensive
encephalopathy are CCs.
Dementia vs. Encephalopathy
A common clinical and coding problem is establish and validating the diagnosis of encephalopathy
when the patient with preexisting dementia is admitted with an altered mental status. This may
represent simple progression of dementia or alternatively encephalopathy imposed on baseline dementia.
The distinction should be relatively simple. If the patient with dementia experiences an acute or
subacute mental status alteration associated with metabolic or toxic factors and returns to baseline status,
an encephalopathy was superimposed on preexisting dementia. If no toxic or metabolic factors are
evident, or if the patient’s mental status does not improve during the hospitalization, encephalopathy is
unlikely.
Delirium vs. Encephalopathy
Many physicians consider delirium and encephalopathy as essentially the same thing. However, from a
coding perspective, delirium is classified as a mental disorder or as a symptom: encephalopathy is
recognized as a specific neurologic diagnosis that identifies toxic and metabolic states affecting the
brain.
For precise clinical documentation and correct coding, the diagnostic term encephalopathy is preferred
for describing mental status alteration when due to toxic or metabolic causes. The term delirium is best
reserved for psychiatric conditions unrelated to underlying systemic conditions.