Not Otherwise Specified (NOS) and Not Elsewhere Classifiable (NEC) diagnosis

Not Otherwise Specified (NOS)

Only use “NOS” codes when the documentation is insufficient to code to a more specific code.  This is synonymous with “Unspecified”.

Example:  A provider note indicates the patient has “otitis media.”  Code 382.9, Unspecified otitis media, becomes the appropriate code if the diagnostic statement or record lacks the additional information, such as purulent or serous.

2.1.4. Not Elsewhere Classifiable (NEC)
Use NEC codes when there is no specific code in the classification system for the condition, even though the diagnosis may be very specific. 

Example:  008.67 Enteritis due to Enterovirus NEC (Coxsackie virus, echovirus; excludes poliovirus).  In this example, this code would be reported even if a specific enterovirus such as echovirus had been identified, because ICD-9-CM does not provide a specific code for echovirus