The “code first” note is your hint that two codes may be needed, along with sequencing direction. The “code first” note is an instructional note.
If you see “in diseases classified elsewhere” terminology you will assign two codes, with the manifestation code being sequenced after the underlying condition. The “in diseases classified elsewhere” (manifestation) code is actually part of the code title. The code with “in diseases classified elsewhere” documented can never be used as a principal diagnosis.
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“Certain conditions have both an underlying etiology and multiple body system manifestations due to the underlying etiology. For such conditions, the ICD-10-CM has a coding convention that requires the underlying condition be sequenced first, if applicable, followed by the manifestation. Wherever such a combination exists, there is a “use additional code” note at the etiology code, and a “code first” note at the manifestation code. These instructional notes indicate the proper sequencing order of the codes, etiology followed by manifestation.” (See Reference 1)
When coding Parkinson’s disease with dementia take a look at the alphabetic index: Parkinsonism (idiopathic) (primary) G20, with dementia G31.83 [F02.80]. The brackets mean that the F02.80 code is a manifestation code and would follow the G31.83 Dementia with Lewy bodies code. If you look in the code book tabular code F02/Dementia in other diseases classified elsewhere – you will see that there is a “code first” note under F20 and under the code F02.8x there is “in other disease classified elsewhere” documented. In the tabular, code G31.8x has a “use additional code to identify delirium and dementia w/with behavioral disturbance at the beginning of the G30/Alzheimer’s disease section.
Reference:
1. Coding guideline FY17 (October 2016 – September 2017) Etiology/manifestation conversation (“Code first”, “use additional code” and “in diseases classified elsewhere” notes)
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