Differential Diagnosis: The Backbone of Clinical Decision-Making

Differential diagnosis is a fundamental skill for physical therapists, essential for identifying whether a patient's symptoms fall within our scope of practice or require referral to another healthcare provider. The process can be challenging due to overlapping presentations of musculoskeletal (MSK) and systemic conditions, requiring both critical thinking and clinical vigilance. This newsletter will explore the foundational steps of differential diagnosis, focusing on distinguishing MSK conditions from systemic issues, recognizing red flags, and emphasizing the PT's role in guiding patients to appropriate care.

The Basic Process

A structured differential diagnosis process is vital for effective clinical decision-making and can be seamlessly integrated into a standard PT evaluation. By embedding differential diagnosis strategies into the subjective interview, objective assessment, and reassessment process, PTs can more effectively determine if a patient’s symptoms fall within their scope or warrant further medical referral. This integration ensures a more comprehensive understanding of the patient's presentation while maintaining a focus on both mechanical and systemic considerations. Here's a simple step-by-step guide:

1. Patient history and Subjective Interview: This is potentially the most important key to the differential diagnosis process as it is where valuable information outside of common MSK issues can emerge.

   • Gather detailed information about the symptom onset, duration, location, and intensity.

   • Ask about aggravating and relieving factors.

   • Identify patterns related to daily activities, rest, and lifestyle factors.

   • Listen for signs and symptoms that do not align with typical MSK patterns, such as consistent pain that is unaffected by movement.

2. Pattern Recognition: MSK versus Systemic

   • MSK Injuries- Typically present with a clear mechanism of injury (MOI), localized pain, and symptoms influenced by movement and position. Although, MSK injuries can sometimes come about insidiously with more diffuse, regional pain.

   • Systemic Issues- Often present with diffuse, non-mechanical pain, persistent symptoms, and minimal response to physical interventions.

3. Constitutional Signs and Symptoms and their Importance: These symptoms are non-specific systemic warning signs that, when present, may indicate underlying pathology requiring medical attention. To me the most common and easy to spot include:

   • Fever- Persistent, unexplained fever could indicate infection, malignancy, or inflammatory conditions. Typically, fever is seen as a red flag when an individual has a temperature above 99.5 degrees Fahrenheit for over two weeks. If a patient is an older individual prolonged temperatures below this level can also be a red flag.

   • Unexplained Weight Loss- Unexplained weight loss is often an indicator of systemic disease and can go unnoticed by patients. This fact may indicate malignancy, metabolic disorders, or chronic infection. A loss of more than 5% of a patients body weight in less than six weeks is often the bar used to indicate a red flag.

   • Fatigue: Persistent, unrelenting fatigue not relieved by rest can be linked to systemic conditions such as anemia, cancer, or autoimmune disorders. When an individual experiences fatigue that goes on for greater than two weeks, interferes with their daily activities, and has no reasonable explanation it is considered a red flag.

   • Malaise: A general feeling of discomfort or unease often accompanies systemic illness and should be investigated further when paired with other signs. This vague yet persistent sense of being unwell can be a key indicator of significant underlying pathology, especially when it is persistent, unexplained, and coexists with other constitutional symptoms.

4. Systemic Questionnaires: These can be helpful when constitutional symptoms and clinical findings raise suspicion of systemic involvement. These tools help guide more specific questioning and can support clinical decision-making when referral is being considered.

   Example: A patient presents with persistent right shoulder pain that began without trauma. The pain does not respond to positional changes and worsens at night. Upon further questioning, the patient also reports unexplained weight loss over the past month and persistent fatigue that interferes with their ability to perform work duties. Considering these constitutional symptoms alongside the location of pain, you decide to screen for hepatic involvement using a liver health questionnaire since the liver can refer pain to the right shoulder and systemic signs are present.

5. Physical Examination: This is our bread a butter and where we can begin to piece together the information we gathered from the patient’s subjective interview.

   • Perform a standard evaluation including observation, palpation, range of motion, strength testing, and special tests.

   • Confirm if findings match expected patterns for common MSK conditions. Do not only look at tests that confirm a diagnosis on a referral. Its our job to be thorough examiners and you never know how well a patient was evaluated previously or if they even were. With direct access to PT services more and more patients are seeking our expertise without a physician referral in the first place.

   • If symptoms persist despite intervention, consider non-MSK sources and re-evaluate. If upon re-evaluation little to no progress is made with therapeutic intervention, consider a referral back to the primary care physician (PCP).

6. Evaluating Atypical Findings:

   • When the subjective and evaluation information don’t line up with common MSK conditions or symptoms persist despite treatment, consider systemic sources.

     • To really throw a wrench into the works we must remember too that systemic pain can often mimic MSK pain due to referred pain patterns. For example, hepatic issues may refer pain to the right shoulder, while cardiac conditions can refer pain to the left arm and jaw. This overlap can make it challenging to differentiate between true MSK dysfunction and systemic involvement, emphasizing the need for thorough screening.

     • I have included a photo of common systemic/visceral pain referral patterns that are often mistaken for MSK issues. Occasionally, when the systemic issue is dealt with the patients MSK complaints can be totally resolved.

   • Be prepared to ask difficult and even uncomfortable questions, such as:

     • Have you noticed any changes in bowel and bladder function?

     • Have you noticed any excessive sweating or night sweating?

   • Always approach patient questioning with professionalism and empathy. While certain health-related questions may feel uncomfortable to ask, they are essential for ensuring comprehensive care. Patients generally appreciate thorough assessments and trust you as a competent healthcare provider. Being transparent and direct while maintaining sensitivity helps build trust and ensures the patient feels supported throughout the evaluation process.