The cervical spine usually has a nice forward, or lordotic, curve.  However, many patients can present with a reduced or even reversed (kyphotic) cervical curve that is acquired due to poor posture.  The old ICD-9 code, 737.10 Kyphosis (acquired) (postural), was probably the best choice.  But it was rather general.  ICD-10-CM offers the following choices in the M40 category, which all specify the cervical or cervicothoracic region:

• M40.00 Postural kyphosis, site unspecified
• M40.03 Postural kyphosis, cervicothoracic region
• M40.12 Other secondary kyphosis, cervical region
• M40.13 Other secondary kyphosis, cervicothoracic region
• M40.202 Unspecified kyphosis, cervical region
• M40.203 Unspecified kyphosis, cervicothoracic region
• M40.292 Other kyphosis, cervical region
• M40.293 Other kyphosis, cervicothoracic region

The M40.0- codes seem like the best option since they include the word "postural", however, for some reason, there is no code designated for the cervical region.  If the kyphosis extended from C3-C6, there is no code that specifically describes this condition.  The unspecified code, M40.00, would probably be the best choice in this case.  If the kyphosis extended down to T1, then M40.03 would be the best option.  

The M40.1- codes are for kyphosis that is caused by some other condition.  Though not specifically stated, it may be wise to also code for whatever the primary condition is which led to the kyphosis.  If posture caused the kyphosis, then the M40.0- codes should be used.

The remaining options, "unspecified", and "other" would be used if the type of kyphosis is not documented, or if it were documented as something other than postural or secondary.  (See the article from 10/27/15 entitled When can I use "unspecified codes?  What about "other"? for more on these types of codes.)

Note that none of these options pertain to "hypolordosis", which is a reduced, but not reversed curve.  It would be incorrect to use one of the these codes in that case.  If the provider feels that that condition is important enough to include on a claim form, then R29.3 Abnormal posture might be the best option.  However, this code is from the signs and symptoms chapter and therefore not very helpful in establishing medical necessity by providing a definitive diagnosis.  It may be better to just document this information clearly in the record.