Here are a couple of explanations I found for you, hope it helps:
The CMS and CPT history components are the same.
History documentation includes the history of present illness (HPI), review of systems (ROS) and past medical, family, and social history (PMFSH). These elements may be documented separately or contained within one statement. The E/M guidelines recognize four levels, and all require a chief complaint:
Problem Focused: Brief history of present illness or problem
Expanded problem focused: brief HPI, problem pertinent ROS.
Detailed: Extended HPI, problem pertinent ROS plus a limited number of additional systems. Pertinent PMFSH related to the patient's problems.
Comprehensive: extended HPI, ROS that is directly related to the problems identified in the HPI plus all additional body systems, and a complete PMFSH.
Exam documentation may be body area or organ system based, except a comprehensive exam which is based on organ systems only. The extent of documentation will depend on the nature of the presenting problem. Both CMS and CPT use the following definitions:
The Exam components are defined as:
Problem focused: a limited examination of the affected body area or organ system.
Expanded problem focused: a limited examination of the affected body area or organ system and other symptomatic or related organ system(s).
Detailed: an extended examination of the affected body area(s) and other symptomatic or related organ system(s).
Comprehensive: a general multi-system examination or a complete examination of a single organ system.