Health data standards and systems

Patient had abnormal limb movements, due to a particular drug.
Following the index - Abnormal - movement, it takes me to a G code - disorder; being a non-essential modifier. However, the correct code seems to be an R code. Should disorder be an essential modifier?

The VICC referred this query to the NCCH suggesting that NCCH alter the default to R25.8 Other and unspecified abnormal involuntary movements. The NCCH provided the following response:
NCCH agrees that 'abnormal limb movement', not specified as a disorder, should be classified as:
R25.8 Other and unspecified abnormal involuntary movements

The indexing of 'Abnormal, movement' is consistent with ICD-10. NCCH will submit a proposal to WHO URC to amend the index.
The VICC received the following updated advice from the NCCH:
After further review, NCCH supports the assignment of G25.9 Extrapyramidal and movement disorder, unspecified for the case cited in the query (abnormal limb movement, due to a drug).

Follow the index pathways:
Abnormal
- movement (disorder) (see also Disorder, movement) G25.9

Disorder
- movement G25.9
- - treatment-induced G25.9

This advice supersedes advice published in the Third Quarter 2005-06 ICD Coding Newsletter.