One of the first debates in my clinical psychology class in college (that has obviously made an impression and stuck with me!) was about the pros and cons of a categorical system of diagnosis for mental illness (vs. a system that recognizes diagnoses along a continuum)¹. Diagnoses for psychological illness are described in the “Diagnostic and Statistical Manual of Mental Disorders (DSM–5)”

Similarly, medical diagnosis are described by certain recognized “criteria” or standards set out by clinical experts or researchers. So, the idea is that you either have a diagnosis or you don’t. Yes or No. This is how we are taught as physical therapy students (at least in our formal education): the goal is to figure out the “right” physical therapy diagnosis for the patient you are working with during your examination.

Some Pros of Categorical Diagnosis:

1. They can guide treatment options
2. They can provide an organized system for reimbursement for medical services
3. They can provide a way to study certain evaluation and treatment techniques for similar patients (i.e., same diagnosis)
4. Patients may find solace in “knowing what is wrong”

We spend a lot of time in our physical therapy education discussing and practicing “differential diagnosis” or the idea of distinguishing between similar diagnoses. The main benefit to this (from my student perspective and understanding) is to guide effective treatment decisions. That is, if you can correctly identify a dysfunction in structure or function- then theoretically your treatment of that dysfunction will be more effective because you can treat the root of the problem.

What are the Cons of Categorical Diagnosis?

We must also keep in mind that there are also downsides to applying a diagnostic label to a person. First of all, mistakes can be made in diagnosis and to label someone as “having” a disorder or diagnosis may be harmful in some cases. A common example of this is patients who seem to “own” or “overidentify” with their diagnosis or become fixated on a structural issue limiting their functional recovery or progress. This second example of over attention to structural findings is quite common with low back pain patients. Despite studies that have shown very little correlation between structural injury and findings of imaging techniques ⁵, the idea that one has a “bulging disc” or has “thrown out” his or her back is still pervasive.

Some Cons of Categorical Diagnosis:

1. A patient may “overidentify” with a diagnosis
2. Diagnoses may be difficult to change once applied
3. Health Care professionals can diagnose incorrectly
4. An incorrect diagnosis may limit treatment to ineffective options

Words are not completely innocuous. For example, research has shown that words can affect outcomes in pain patients: (http://www.bodyinmind.org/talking-about-pain/). To me, the word “chronic,” conveys a resistance to change and a permanence. Is telling people that they have chronic pain contributing to the fact that it is so hard to treat?

What are your thoughts on categorical diagnosis in medicine or physical therapy practice?

…Read on if you are interested in an example I have encountered recently regarding differential diagnosis in a Neuro PT setting:

I am currently working as a student physical therapist in a setting treating neurologic patients. One of the differential diagnosis decisions that I have been learning about is that between Primary Lateral Sclerosis (PLS) and “Stiff Person Syndrome” (SPS). Both have similar presentations in some ways: both are rare, present with primarily motor system dysfunction including rigidity of the trunk/lower extremities.

One article⁴ summarizes some of the key characteristics of PLS: Primary Lateral Sclerosis (PLS) is a type of motor neuron disease characterized by upper motor neuron signs and the absence of lower motor neuron signs. This is different from the more common motor neuron disease Amyotrophic Lateral Sclerosis (ALS) that usually presents with a mix of upper and lower motor neuron signs. In simple terms, the difference is whether nerve cells in your brain or spinal cord are affected vs. nerve cells that go to your periphery and take information from/to skin or muscles.

Impairments commonly seen in PLS are stiffness/hypertonia, mild weakness, balance/coordination deficits (contributing to increased risk/incidence of falls), spasticity, hyperreflexia, pathological reflexes, and possible bulbar symptoms (e.g., dysphagia, dysarthria). In contrast with ALS, PLS often presents with more stiffness, less muscle wasting, and a slower and less aggressive progression of disease (estimated symptom duration of about 7.5-15 years vs. ALS where 5 years is average age for mortality). PLS symptoms usually begin in the legs and progress to other body regions. PLS is a diagnosis of exclusion and is based on clinical presentation of most often lower extremity stiffness, > 4 or 5 years of symptoms, and upper motor neuron signs (spasticity, hyperreflexia, etc.) in the absence of family history of disease, sensory impairment, or significant muscle atrophy.

Differential Diagnosis: PLS vs. SPS

A potential differential diagnosis with PLS is Stiff Person Syndrome (SPS), which presents with severe stiffness/rigidity (axial and extremity), possible hyperreflexic DTRs, and normal sensory exam similar to PLS. Unique to SPS are anti-glutamic acid decarboxylase (GAD) antibodies, which are often used as part of the diagnostic decision. Key differences in SPS presentation also include: usually no pathological reflexes and normal motor exam (no weakness)^2,3,4.

I am not sure that distinguishing between these two disorders is absolutely necessary in order to help these patients in a physical therapy setting. There can be different courses of the diseases, but I believe we can still help these patients by treating the impairments (i.e., issues that we identify in function/structure) for that particular individual.

References:

1.     Lilienfeld SO, Marino L. Mental disorder as a Roschian concept: a critique of Wakefield’s “harmful dysfunction” analysis. Journal of Abnormal Psychology. 1995; 104 (3): 411-20.

2. Nalbantoglu M, Battal H, Kiziltan ME, Akalin MA, Kiziltan G. Stiff Person Syndrome with Pyramidal Signs. Noro Psikiyatri Arsivi. 2016;53(2):188-190.
3. Sarva H, Deik A, Ullah A, Severt WL. Clinical spectrum of stiff person syndrome: a review of recent reports. Tremor and Other Hyperkinetic Movements. 2016;6.
4. Statland JM, Barohn RJ, Dimachkie MM, Floeter MK, Mitsumoto H. Primary Lateral Sclerosis. Neurologic Clinics. 2015;33(4):749-760.
5. Wiesel SW, Tsourmas N, Feffer HL, Citrin CM, Patronas N. A Study of Computer-Assisted Tomography: I. The Incidence of Positive CAT Scans in an Asymptomatic Group of Patients. 1984; 9(6).