Medical doctors make diagnoses based on patient symptoms and clinical presentation (e.g., low back pain, lumbago with sciatica). When there is an underlying problem such as infection, tumor, or fracture, then the diagnosis reflects the pathologic process present.
Physical therapists confine their diagnoses to the musculoskeletal system in what they call human movement impairments. The way we move in everyday life during our daily activities may not be caused by a specific pathologic process. Instead, over time with sustained postures and repeated movements, we may eventually develop problems and pathologic abnormalities.
So both the viewpoint and the approach of these two health care professionals (physicians and physical therapists) is very different and thus requires different names of diagnoses. There are also diagnostic categories set up for billing purposes that may direct and guide the naming of a diagnosis. For example, there are ICD and ICF codes used to bill for services.
ICD stands for International Statistical Classification of Diseases and Health Related Problems. ICF refers to the World Health Organization’s International Classification of Functioning, Disability, and Health codes. There are both ICD and ICF codes used to name/describe low back pain.
There is a move now in health care for all organizations to use the ICF codes so that no matter where a patient is treated (anywhere in the world), the same codes will be used for everyone. This will also help facilitate consistency in research efforts.
Your physician is using the ICD code of lumbago with sciatica to best describe your problem with that system. Your physical therapist is giving a name to your condition that best describes it using the human movement system descriptors. Both are correct when coming from the two different perspectives, billing codes, and way the problem will be treated.