ICD-10 Code B27.81 – Other infectious mononucleosis with polyneuropathy (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B27.81 – Other infectious mononucleosis with polyneuropathy
What it is
This code identifies infectious mononucleosis with associated polyneuropathy, meaning the viral illness is accompanied by nerve involvement affecting multiple peripheral nerves. Use it when the record links the mononucleosis to the neuropathic complication.
Clinical signs
Clinical features vary; refer to documentation. Typical findings may include mononucleosis symptoms such as fever, sore throat, lymph node enlargement, fatigue, plus sensory or motor neuropathic complaints in more than one nerve distribution.
When to use this code
Use B27.81 when the provider documents infectious mononucleosis and specifically states polyneuropathy as a complication or associated condition. The note should clearly connect the neurologic findings to the mononucleosis rather than to another cause. Check documentation if the neuropathy is only suspected.
Do not use for
Do not use this code for uncomplicated infectious mononucleosis without nerve involvement. Also avoid it when the neuropathy has a different confirmed cause, such as diabetes, alcohol use, or another infection.
Coding tip
Code the mononucleosis complication only when the documentation explicitly links polyneuropathy to the infection.