Approach to pathological diagnosis of diseases

How do I approach a question on laboratory diagnosis in pathology?

Dear friends,

As part of your second professional examination, all of you will face a compulsory question on laboratory diagnosis of a particular condition. Here is a basic guide to how to approach such a question.

The questions on laboratory diagnosis may be placed in two ways. Study the following questions carefully:

1. How do you approach to diagnose acute leukemia in the laboratory?

2. A 17 yr boy came to the outdoor with complaints of fever and nodular swellings over neck. On examination, he had marked pallor. How do you approach to diagnose the case in the laboratory?

A quick look will reveal that the approaches of the two questions are different. The first question points to a specific diagnosis and asks about the relevant laboratory investigations needed to establish the diagnosis. The second question gives you a constellation of symptoms and signs and asks you to make a clinico-pathological diagnosis.

Let us first pick up the second question and try to solve it. For all practical purpose, your answer can be divided into the following parts:

• Case summary
• Provisional diagnosis
• Differential diagnosis
• Approach to diagnosis
  

Case summary:

This means you summarise the history and clinical features mentioned in the question in a logical manner so that it can point to a specific diagnosis.

For Q.2 it can be written as follows –

History: a boy aged 17 yrs came with a chief complaint of – a) fever, b) nodular swellings over neck.

Physical examination: marked pallor


Provisional diagnosis (PD):

This means, you write down the most appropriate diagnosis that matches with the given symptoms. The appropriateness will depend on –

• The prevalence of the disease. The commoner the disease more is the chance of the person suffering from it. Remember, rare diagnoses are rarely correct.
• The disease that you choose as your PD should logically explain all the symptoms and signs mentioned in the question.
• Your PD can be different from your friend’s PD. There is no rule of thumb that all PD has to be the same.
  For examination purpose, try to choose the PD from the diseases that are important in your syllabus. This is because examiners will expect you to answer from the chapters you have read. Moreover, the diseases that you read in your syllabus are also the commoner diseases.

For Q2, I can write my provisional diagnosis as follows:

Provisional diagnosis: Acute leukemia, probably ALL


Differential diagnoses (DD):

This means, you list all the diseases (or their complications) that can mimic the signs and symptoms of your PD. Please remember that this is the most important part of your answer. Follow these simple rules to find out the probable DDs:

• Keep your mind open to all possibilities (including relatively rare diagnosis) while searching for DD
  Search for the diseases systemically, i.e. follow a pattern of going through different systems of the body. This will ensure that you never miss a DD
• You can also include complications of a primary disease as a DD
• Remember, your DD can be someone else’s PD!

As for example, let me list the DDs for Q2.

Differential diagnoses:

a) Hematological:

1. Acute lymphatic leukaemia ( your PD is always your first DD)
2. Juvenile CML (in blast crisis phase)
3. Hodgkin’s lymphoma
4. Infectious mononucleosis

b) Respiratory:

1. Pulmonary tuberculosis ( anemia is due to chronic disease)

c) Multisystemic:

1. Septicemia
2. Metastatic carcinoma ( with Lymph Node and Bone Marrow metastasis)


This is how you list your DDs.

Now you might wonder why at all should we bother about the DDs? Because, we need to investigate only when there is some confusion in the diagnosis and we want to rule out the other causes. If we are already sure about a single diagnosis, there will be no need to investigate at all!

Differential diagnosis is a scientific approach by which we can reach at a single diagnosis by clinical and laboratory tests (very much like testing for the acid and basic radicals of an unknown salt in the chemistry lab).


Approach to diagnosis:

This can be done by following four simple steps:

1.Find out the systems of the body that your DDs cover
2.Note down the routine investigations that you do for each systems
3.Note down the specific or confirmatory diagnosis for each of the DDs
4.Now make a chart with the left-most column reading “steps of diagnosis”, and the rest of the columns dedicated to each individual disease. Point down the list of all investigations that you have listed in the above steps. Write down the findings of each disease against each point. If the test is in no way related to the disease, you can expect the finding to be normal. Mention if the finding may change with a complication.

For Q.2, the left column may include the following points:

1) History

2) Clinical features

3) Routine blood examination
· Hb
· TLC
· DLC
· Platelets
· Reticulocytes
· Abnormal cells

4) Bone marrow examination
· Cellurarity
· Nature of myelopoiesis
· Nature of erythropoiesis
· M:E ratio
· Megakaryocytes
· Plasma cells
· Abnormal cells/ parasites

5) Biopsy from the nodular tissue
· HE stain

6) FNAC from nodular tissue
· Pap stain
· Gram stain
· Acid fast stain

7) Blood culture

8) Chest X ray

9) Abdominal CT scan/ USG (to rule out occult neoplasm)



Now in case of Q.1, where the question is straight and simple, (Lab diagnosis of Acute leukemia), follow these steps:

1.List all the pathological types of the disease ( In this case, ALL and AML)
2.Jot out the points for diagnosis as before
3.Jot out the points for diagnosis of complications
4.Now make a chart with the left-most column reading “steps of diagnosis”, and the rest of the columns dedicated to each type. Point down the list of all investigations that you have listed. Write down the findings of each disease against each point. If the test is in no way related to the disease, you can expect the finding to be normal. Mention if the finding may change with a complication.


So, here you go… try and write the entire approach yourselves, and get back to us if you face any problem. You can also email your completed answers to tirthankar82@yahoo.co.in which we can publish with your names.

Till then, take care.

Cheers!