Here is what CPT Assistant September 2006 says about 99078:
Question: A physician performs an office visit individually with four patients who are diagnosed with the same chronic pain disorder. Later that same day, the physician spends 45 minutes with the four patients educating and counseling them as a group. How are these services reported?
AMA Comment: From a CPT coding perspective, the code series 99000-99091 provides
the reporting physician with the means of identifying the completion of special reports
and services that are an adjunct to the basic services rendered.
Codes 99000-99091, Special Services, Procedures and Reports, describe special circumstances under which physician services are performed. None of the codes in this range can be reported separately; rather, these codes are reported in addition to the basic services that are provided.
Many times a physician provides education to his or her patients at the time of the visit. Patient and family education are part of counseling. When counseling dominates (more than 50%) the physician, patient, or family encounter, then time is considered the key or controlling factor to qualify for a particular level of E/M service.
However, code 99078, Physician educational services rendered to patients in a group setting (eg, prenatal, obesity, or diabetic instructions), is reported when physician educational services are provided to patients in a group setting. Although this reporting method reflects the intent of CPT coding guidelines, third-party payers may request that these services be reported differently. It is best to contact the third-party payer for specific reporting guidelines.
As you can see, not much - but they do advise contacting the third-party payer.
Hope this helps somewhat,