Module 6

Beyond the Initial Hypothesis

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What happens after you derive the initial hypothesis, the first cut at the differential diagnosis?

There are two lists you have to keep separate and workable.

• One consists of important findings you know about your patient. These findings you derive from the Chief Complaint (CC), the History of the Present Illness (HPI) and the Medical and Dental Histories (MH and DH).
• The second list is the diseases and conditions in your Initial Hypothesis. For each of the diseases or conditions, you should list the clinical and, if appropriate, radiographic characteristics.

What you do next is compare the lists. In Module 3 part 2 you learned about known information and information needed. If you need to ask your patient more questions to flesh out your known clinical information, do so. If you need to get more radiographs, perform clinical and/or laboratory tests obtain information from old records, do so. Compare the information you have from your book about the diseases and conditions on your initial hypothesis list with the information you know from your patient. Using this comparison method, you should be able to rule out some of the diseases on your list, and retain others for consideration.

Sometimes it is useful to group your list of hypotheses in a way that helps you eliminate possibilities.

• Does your list consist of both malignant and benign possibilities?
• Certain characteristics of your patient's problem may allow you to eliminate all the choices in one group at one time.
• Does your list contain both inflammatory disease and benign tumors?
• Find common elements in several diseases in your list?

There is no set way to organize your list of hypotheses, and it may not be helpful to do so, but experience holds that organizing data is more often helpful than not. Try different alternatives. Your objective is to keep paring your list down by eliminating possibilities.

Two important rules govern paring down your differential diagnosis list (differential diagnosis list):

• Never eliminate a choice without a-reason.
• Be able to defend your decision to include or exclude an item on your list.

Eventually you will get to where you cannot exclude any more diseases based on what you know from non-invasive clinical examinations and history. At this point, the diseases left on your hypothesis list comprise your final clinical differential diagnosis.

How do you arrive at a final diagnosis?

There are a number of possible pathways depending on the nature of the diseases in your final clinical differential diagnosis:

1. Treat and exclude by treatment results: This path means you have a final clinical differential diagnosis list of diseases that respond to different treatments. Some may not respond to treatment at all.

For example: Both lichen planus and Candidiasis can present as white lesions on the oral mucosa. Your final clinical differential diagnosis list for your patient's condition is down to lichen planus and Candidiasis. Your biopsy report is equivocal: some characteristics of lichen planus, but a few fungal organisms in the specimen as well (this is not an unrealistic scenario).

Here's your plan:

• Treatment for lichen planus is steroids and Candidiasis responds to an antifungal medication. You wouldn't want to treat Candidiasis with a steroid (it would make the Candidiasis worse), so combining the medications is not possible.
• Solution: treat definitively for Candidiasis with an antifungal medication (this would not make the lichen planus worse).
• After the course of treatment is over, biopsy any lesions remaining to see if they are more definitively lichen planus.
• If the all lesions disappear after treatment for Candidiasis, then the assumption is that it was only Candidiasis.

Thus you have treated and excluded one hypothesis by the results of the treatment. Carefully evaluate your hypothesis list to be sure that treating for one condition will not make the others worse.

2. Biopsy: A biopsy consists of surgically removing a portion of or the complete lesion and submitting the specimen to a pathologist for microscopic examination and diagnosis.

The decision to use biopsy as a diagnostic tool depends on the health of the patient, the expertise of the clinician, the nature of the lesion (consistency, location, size etc.), other lesions on your list and your realistic judgement that histologic examination will lead to diagnosis.

A biopsy can be either an incisional biopsy (taking a piece of the lesion), or an excisional biopsy (removing the whole lesion). Your choice as to which of the alternatives is appropriate depends on issues that will be discussed more thoroughly in your surgery course. For the purposes of this module, biopsy will be considered to include both incisional and excisional type. Biopsy will be one of the most useful ways you will have to determine a final diagnosis. All biopsies are sent to an oral pathologist for microscopic examination and a report for your records.

3. Exfoliative Cytology: To take a cytologic smear, you harvest cells from the surface of a lesion by scraping them off with a tongue blade or a brush. Then you smear them on a microscope slide, fix them with 95% alcohol and send the slide to a lab. At the lab, the slide is stained with the Papanicolaou Stain and read by a pathologist to characterize the nature of the lesion from which the cells were harvested or make a diagnosis. You only use cytologic smear as a diagnostic tool when you are reasonably confident that you will achieve a result. Use exfoliative cytology on some mucosal leukoplakias (white plaques) that do not rub off, red and white lesions (combinations of erosions and leukoplakias) and white lesions that do rub off, for example suspected Candidiasis. We do not use exfoliative cytology for lesions that are underneath the epithelial surface, for example a fibroma. There is no way to scrape the cells of the actual lesion. (To learn more about oral exfoliative cytology, click here: Cytology)

4. Referral: This pathway is usually taken when your final clinical differential diagnosis includes lesions that would be treated by a specialist. You refer if your expertise does not extend to the level demanded for treating the diseases you are considering, or if the problem your patient has is not a dental problem and you wish to refer to a physician to rule out or treat the systemic disease. Referral is never meant to be a way to dump patients whom you simply don't wish to treat.

Follow up and evaluation of treatment is an important aspect of your practice. Obviously you should follow a patient under active treatment to be sure the treatment you have prescribed or performed is working. Follow up is also important from the patient's point of view. Patients have the opportunity to ask questions or clear up misunderstandings.

• Follow up is important from the standpoint of your ongoing assessment of your practice.
• Are the treatments you recommend for various conditions working?
• When you see a number of similar cases, do you treat them the same way, or do you treat them differently?
• What regime is successful and what isn't?
• These are important ways to tell if you are maintaining a successful practice.

You have now come to the end of the modules that prepare you with the diagnostic skills to begin to complete the cases in the laboratory portion of this course. Go to the course index page and look at the Example Case. Then you can try the 7 test cases you need to complete before you finish this course.

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Last Modified: June 14, 2001
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