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.

Real World Application and Case Study

The following patient scenario is a case study from the Journal of Orthopaedic & Sports Physical Therapy. I would encourage you to review this case study independently as it’s a great example of why the differential diagnosis screening is vital for PT’s so patients get the care they need. As you read through the case study I’d encourage you to note any red flags you see and any patterns in the patient’s presentation that are atypical. Below I provide my own synopsis and takeaways from the case study.

Link to Case Study:https://www.jospt.org/doi/epdf/10.2519/jospt.2005.35.10.651

Patient History: A 45-year-old male presented with intermittent left-sided low back pain extending into his posterior thigh, accompanied by occasional tingling along the front of his left lower leg. His symptoms were aggravated by prolonged sitting, standing, lying supine, coughing, and sneezing, while heat application and ibuprofen provided temporary relief. Pain was most intense in the evenings and sometimes disrupted his sleep, though he could typically find a comfortable position to fall back asleep. He denied any history of cancer, diabetes, or significant weight changes and reported normal bowel and bladder function. His occupation involved long periods of sitting and occasional lifting, with no known injury preceding his current symptoms.

Examination Findings:

1. Gait: Mildly antalgic, especially when bearing weight on the left side.

2. Trunk Mobility:

   • Active lumbar extension and left-side bending were limited and reproduced left-sided low back pain.

   • Flexion and right-side bending were within normal limits and pain-free.

3. Neurological Findings:

   • Reduced strength in the left hip flexors and knee extensors during myotome testing.

   • Deep tendon reflexes (Achilles and Patellar) were hyporeflexive B.

4. Passive Range of Motion (PROM):

   • Significant restriction in left hip adduction when flexed to 90 degrees.

   • Pain reproduced in the posterior thigh during adduction.

   • All other hip motions (flexion, internal, and external rotation) were symmetrical and pain-free.

5. Key Concern:

   • The restricted left hip adduction was inconsistent with a typical capsular pattern, which usually limits flexion, abduction, and internal rotation.

   • Abnormal neurological findings such as hyporeflexia and mild myotomal weakness at the L3 and L4 levels.

   • This atypical presentation raised concerns for non-mechanical pathology requiring further medical evaluation.

Treatment Results: The patient's treatment began with lumbar rotational mobilizations and home exercises focusing on lower trunk rotation and left hip stretching, aimed at improving mobility and reducing pain. While the patient experienced brief pain relief, his overall condition remained unchanged, with persistent pain and restricted left hip mobility. Over the next month and five therapy visits, his symptoms worsened, including increased pain, reduced sitting tolerance, and a more pronounced antalgic gait requiring the use of a cane. Concerned about the patient's declining function and lack of response to conservative care, the physical therapist recommended a medical follow-up, leading to imaging and lab tests that revealed concerning abnormalities. Subsequent testing confirmed a diagnosis of metastatic small-cell lung cancer with extensive bone involvement, and the patient passed away five months later despite chemotherapy treatments.

Takeaways: This case underscores the importance of recognizing when a presentation extends beyond typical MSK patterns. Night pain, progressive symptoms, and a lack of response to conservative care were critical indicators for referral. While some of the patient's symptoms initially responded to treatment, clinical vigilance and the PT's responsibility to ensure appropriate care ultimately led to proper diagnosis and intervention.

Always Be Vigilant!

Differential diagnosis is a critical component of physical therapy practice, ensuring that patients receive appropriate care and that serious conditions are not overlooked. As physical therapists, we have a responsibility to recognize when a patient’s presentation extends beyond typical musculoskeletal patterns and requires medical referral. The case study presented serves as a reminder that staying vigilant, especially when symptoms do not respond as expected, can make a significant difference in a patient’s health outcomes. Prioritizing thorough patient history, screening for red flags, and understanding both MSK and systemic presentations helps us better serve our patients. Let’s continue to refine our skills and ensure we’re providing the highest standard of care.

What red flags stood out most to you in this case? How would you approach a similar scenario in your clinical practice, and what systemic conditions might you suspect? Share your thoughts and experiences in the comments below—your insights can help the entire community grow!

References:

1. Heick LJ. Differential Diagnosis for Physical Therapists: Screening for Referral. 7^th ed. Elsevier; 2023.

2. Ross MD, Bayer E. Cancer as a cause of low back pain in a patient seen in a direct access physical therapy setting. J Orthop Sports Phys Ther. 2005;35(10):651-658. doi:10.2519/jospt.2005.35.10.651

Disclaimer:

I am a current Doctor of Physical Therapy (DPT) student sharing information based on my formal education and independent studies. The content presented in this newsletter is intended for informational and educational purposes only and should not be considered professional medical advice. While I strive to provide accurate and up-to-date information, my knowledge is based on my current academic and clinical rotations and ongoing learning, not extensive clinical practice.