Textbooks often fail to properly prepare physical therapy students and novice healthcare professionals in forming a differential diagnosis. That’s mainly due to the contrast between textbook scenarios or typical presentations and real-life bedside clinical presentations.
The process of establishing the final diagnosis is not a matter of intuition or mere experience but it’s a scientific process. Hence, it requires a scientific approach.
In physical therapy, the diagnosis is not entirely dependent on the physiological structures or the compromised anatomical regions. Rather, it’s focused on how the condition affects the patient’s function.
That’s why the traditional frameworks for establishing the differential diagnosis used in other medical fields might not apply in PT.
If you’re a physio who struggles with narrowing down the diagnosis or if you’re looking to create an efficient system to speed up your diagnostic steps, then this article is for you.
Here, we’ll cover the basic steps and discuss the top three strategies that can help PT students improve their differential diagnosis skills.
Differential Diagnosis – An Overview
Differential diagnosis (DD), or simply differential, is also sometimes referred to as clinical reasoning.
It’s a collection of potential diagnoses that may explain the symptoms of your patient. According to Dr Eric Strong, “you should prioritize [the diagnoses] in the descending order of likelihood”.
The process of creating the differential begins at the time of history taking and objective assessment where the physical therapist or health care provider gathers the clues based on attentive listening and testing. And then generates multiple possible diagnoses for the patient’s condition.
Your DD should include the top most relevant conditions that match the patient’s presentation.
It’s important to note that you can’t form the same differential with all the patients presenting with similar symptoms. That’s because each patient has some standout features which can be their line of work, travel history, family medical history and so on.
It’s important to note that you can’t form the same differential with all the patients presenting with similar symptoms. That’s because each patient has some standout features.
That’s why the differential diagnosis should be specific to each patient. Also, you should be careful not to get distracted by these unique features and stay concentrated on the key features.
Remember that the differential can take a while. And you may not have all the answers in one session. So don’t rush the process because your treatment largely depends on the diagnosis.
Steps for Creating a Differential Diagnosis in Physical Therapy
An organized and structured approach can make the process of creating the DD much more efficient. It can also help you narrow down the most relevant diagnosis quicker, saving your and your patient’s time.[i]
Here are the five steps you should take while creating a differential:
1. Acquire data
Listen attentively to the patient’s history and ask for further elaborations when you need to. You can also acquire data from past medical records, scans, lab reports and family members or caregivers.
2. Separate relevant information that can help you in eliminating diagnoses
An important step while collecting data is to separate the relevant information from the rest of the history.
For example, if the patient complains of shoulder pain during abduction then that will be a key feature. But the severity of the pain with the different amount of weight lifted to elicit the pain may not be key features for now as that doesn’t necessarily help you in forming the differential.
3. Develop the problem representation
This is where you translate the history and the findings of the examination into a syndrome if possible.
Or develop a single or few sentences that summarize the condition. Include only the most useful information here.
The problem representation could include age, gender, pain location, comorbidities, and the chief presenting complaint.
For example: a 24-year-old male athlete with an insidious localized dull ache in the right ankle or a 57-year-old female with limited ROM and progressive pain in the left shoulder post-mastectomy are problem representations as these contain only the most relevant information.
4. Pick a framework.
This step is different for the different healthcare departments. For the physical therapy setting, you can choose from any of the strategies we’ll discuss below.
Physicians can select the physiological or anatomical frameworks. But these generally don’t fit well for the conditions presented in PT environments. But the goal remains the same which is to categorize the alternative diagnoses and work systematically to rule each of them out.
5. Apply the key findings to the framework.
Here, you use your knowledge of the diseases to check the likelihood of the diagnosis being the definitive diagnosis for your patient. And remove the hypothesis that has the minimal probability of being accurate.
3 Strategies for Creating a Differential Diagnosis in Physical Therapy
Now that you know the basic steps for creating a differential, let’s discuss the three techniques that can significantly improve your process:
1. Symptoms complex
A great strategy for DD that most experienced physical therapists use is the symptoms complex.
What you do here is cluster symptoms in your mind while the patient is giving the history. The goal here is to de-prioritize the other information such as the demographics and unique features and keep the focus on the symptoms.[ii]
What you do here is cluster symptoms in your mind while the patient is giving the history.
You shouldn’t use this strategy alone while creating your differential because it neglects some critical information that might influence your diagnosis.
However, it’s a good technique for developing DD because disorders are easy to recognize once you cluster the symptoms.
2. Recall Local Structures and their Functions
This technique is highly useful for novice PTs since the majority of the conditions we treat include some form of muscle injury or disorder.
It works best with neurological and muscular-skeletal disorders and when the patient complains of localized pain.
For this strategy, you have to recall the structures located in a particular area while taking the patient’s history. These can be muscles, nerves, ligaments, tendons and joints. Then recall the functions of each of these and match them to the patient’s presentation.
For this strategy, you have to recall the structures located in a particular area while taking the patient’s history.
For example, if the patient describes a radiating pain then you could shift your focus towards the nerves in the region. Or if there is stiffness and throbbing then you could look at the muscles, ligaments or tendons.
The structures you narrow down here should guide the type of special tests you’ll choose to rule out or confirm certain diagnoses.
Next, you could also link the mechanism of injury to the region and think back to what structures might have been damaged because of the injury.
Let me elaborate with an example. Suppose a 62y old patient complains of wrist pain and numbness. The symptoms are predominantly located in the middle finger, index finger and thumb. Recently the pain has started to radiate up the arm as well.
So based on this history, you can recall the local structures primarily the nerves innervating the symptomatic area and begin special tests to confirm your diagnosis.
3. Use A Reasoning Strategy: If – Then – But – Therefore
In this approach, you formulate arguments for and against all the different diagnoses. So once you have all the necessary information, you could check to see which conditions best match the patient’s presentation.
In this approach, you formulate arguments for and against all the different diagnoses.
For example: if the patient complains of shoulder pain in overhead activates, then shoulder impingement may be the case, but the Hawkins / Kennedy test was negative, therefore we need to look for an alternative diagnosis.
You might not even have to wait until the end of the intake to do this as you gain more clinical experience. Because then you could rule out or confirm the hypothesis while doing the initial assessment.
If you’re able to quickly run the if-then-but-therefore formula in your mind then it can help guide you in which questions to ask your patient. Otherwise, you can ask your additional questions at the end once you’ve narrowed down your DD, or in the next session.
For this technique to work though, you’ve got to have some factual information stored in your brain so you know what questions to ask next.
In other words, you need to know enough about disorders and PT conditions that you can systematically eliminate hypotheses based on the information available and the new information you get by asking questions.[iii]
You should take one possible diagnosis at a time. Also, don’t rush the process and prematurely finalize a diagnosis. Even if you’re fairly certain about one, take your time in checking your alternative diagnosis by the if-then-but-therefore formula.
Creating a Differential as A Student PT – The Takeaway
The process of creating a DD begins with collecting data, sorting out the relevant details, creating a problem list and matching them with various disorders or syndromes.
There are a few techniques that you can use to systematically reach a final diagnosis. But you can’t always use one technique alone.
Sometimes the strategies are helpful to guide you to a diagnosis but then you have to deviate from it. For instance, in the example I mentioned in the second strategy above, you can’t only focus on the local structures. Otherwise, you might miss that the carpal tunnel is actually a consequence of arthritis.
That’s why you must use these as guidance tools and modify the technique as you go. You can even switch between approaches while forming the differential diagnosis of the same patient.
With time and practice, most physical therapists develop memory schemes for various common conditions and the differential diagnosis process becomes a routine.