Differential diagnosis

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Differential diagnosis (sometimes abbreviated DDx or or ΔΔ) is the systematic method used to identify the disease causing a patient's signs and symptoms. The term has become somewhat famous (or at least more widely recognized) because of the popular Fox Network medical drama television series House.

The method of differential diagnosis was first suggested for use in the diagnosis of mental disorders by Emil Kraepelin. It is more systematic than the old-fashioned method of diagnosis by gestalt (impression).

The Core Process of Differential Diagnosis

The patient presents with symptoms A and B. The diagnosistician creates a list of diseases, disorders and syndromes that include symptoms A and B. Let us imagine there are only three "disease processes" that feature both symptoms. Let us call them Conditions 1, 2 and 3.

• Condition 1: A, B, C
• Condition 2: A, B, C, D
• Condition 3: A, B, E

The diagnostician now tests for the presence of symptom C. A positive result would support a diagnosis of Condition 1 or 2, and would rule out the possibility of Condition 3. If the client tested positive for C, a test for D could be used to differentiate between Condition 1 and Condition 2. If the client tested negative for C, a test for E would confirm the diagnosis of Condition 3.

The Practical Application of Differential Diagnosis

Before a psychiatric or psychological condition can be treated, by one of the various psychological therapies and/or by psychotropic medications, a mental illness must first be identified correctly.

The diagnosing physician begins by observing the patient during an extended interview process. The patient is observed for signs and is asked for a list of symptoms. A detailed history is taken and questions are asked about the patient's present condition and circumstances. A thorough assessment of all possible supports and stressors and supports in the patient environment is made. When it is possible, a patient's family member might help in gathering the raw materials of a differential diagnosis of mental illness.

The term differential diagnosis refers a process of elimination that progressively weeds out the impossible and less probable, so a remaining list is created of the possible and the more probable.

All the raw materials have been elicited, recorded and evaluated. All the possible psychological and psychiatric conditions that might be suggested by the presenting constellation of signs and symptoms are considered. Then further questions and observations will attempt to narrow down the possibilities.

Eventually, the psychiatrist will be reasonably satisfied that the single most likely cause has been identified. Once a provisional or working diagnosis is reached, a course of therapy is prescribed. If the patient's condition does not improve, the diagnosis and therapy must be reassessed. A change of diagnosis might be a wise step or perhaps a change in therapies will seem in order.

Differential Diagnosis in Mental Illness

With a sore throat or a hurting stomach, diagnosis is usually quickly reached. Symptoms elicited and recorded. A tongue blade and light to examine the throat for swelling, redness and pus, a manual palpation of the stomach for guarding, rebound tenderness, auscultate for bowel sounds. A throat culture taken. A CBC and UA to test for the presence of infections.

But with mental conditions, whether psychological or psychiatric, there are very few diagnosistic exams or tests to rule in or rule out a given diagnosis. This will be less likely true in the decades to come what with all the current neuropsychiatric research, but for now, differential diagnosis of mental illness remains more art than science.

Because of this, the skill level of the diagnostician is a vital component of psychiatric diagnosis. So too is the process of differential diagnosis. One thing a differential diagnosis takes into account is how likely a particular diagnosis is. For instance, in a person under 65, one puts Alzheimer's further down on the list of possibilities and more closely pursues other possible sources of dementia and memory loss. Again, when a person presents with serious depression with no obvious causation, one still investigates for more common depressive triggers before ordering tests to rule out pancreatic cancer.

One of the most confusing tasks in psychiatric differential diagnosis is that of determing the presence of personality disorders. For instance, in determining whether the narcissistic personality disorder is present, the psychiatrist must first identify whether, among others, psychopathy, bipolar disorder, Asperger's Syndrome, ADHD and/or addictions might be either the primary cause of the symptomatology, not present at all, or might exist as codiagnoses. Until all this is done

With mental illness, psychological or psychiatric, differential diagnosis will, more often than in medicine, use the response to medications to rule in or out a given diagnosis. If a person presents with depression, antidepressants might help, but if that patient has Bipolar I and is presenting with depression, those same antidepressants might trigger an agitated, rageful or manic episode. This would immediately rule out simple depression and would strongly suggest bipolar illness.

A person presenting with a great deal of nervousness, anxiety and feelings of dread might seem to need an anxiolytic (a tranquilizer). However, if that person is given diazepam, and then reports an overwhelming depression the next day, perhaps even with suicidal ideation, then what you have is not anxiety, but a depression, masked by anxiety, that mandates treatment for depression, not anxiety.

A patient presenting with complaints of sleeping her life away and retreat from an outside life may suggest many things, but the diagnosis of another atypical depression might be missed. The right medication will have her actively engaged in life in little time. Gross obesity and lack of appetite and thinness must likewise be investigated from many directions to determine if an eating disorder exists or if depression, anxiety, a medication or a medical condition might be at fault.

The goal in treatment of all the various mental illnesses and conditions is to return the individual to maximum functionality. The goal is for the person to have stable working relationships within the family, wider social networks and at work. Insurance no longer pays for years of weekly supportive appointments for chronically unhappy patients. Today, results are what counts. A good working diagnosis ensures that the best possible psychotherapy approach can be selected and that the proper medications can augment and reinforce that psychotherapy.

Additional material

Papers

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External links

• DiagnosisPro - Differential Diagnosis Tool.