Differential Diagnosis
In clinical practice, the treating physician makes a provisional diagnosis of the patient’s condition with due consideration of history, symptoms, and signs. That helps him initiate the treatment until the blood work or other imaging modalities confirm the final diagnosis.
To nullify the subjective bias or further broaden the horizon, the physician includes other probabilities, however remote, as possibilities. This ambit of disorders constitutes the differential diagnosis, shortened to DD.
We have read about the four blind men with limited access describing the pachyderm. That the tusker resembles a pillar, rope, winnow, or weapon sounds ludicrous only because the entirety was not considered. These are different diagnoses (note the plural), not differential diagnosis.
However, it draws two important conclusions in the field of medicine. First, the sum of its parts doesn’t make a whole. Second, mathematics doesn’t apply to medicine despite being an exact science.
From the parable to history:
‘Alexander The Great’ died in Babylon at the age of thirty-two. His cause of death became a topic of debate, retrospectively of course. The list of probabilities could be a treatise on medicine!
A. He drank himself to death, probably due to Alcoholic Liver Disease or Acute Endocarditis or Acute Pancreatitis, was the early surmise.
B. The Infectious Disease Department attributed it to Falciparum Malaria or Salmonella due to his travel conquests.
C. Porphyria or Guaillain—Barre Syndrome was also entered into the database.
D. There was also a conspiracy theory of poisoning by Arsenic or wine made from Veratrum album.
E. His scoliosis and neurological defects were evidence of Klippel-Feil Syndrome, according to other wise men.
It was finally agreed upon that ‘The Prophecy Of Calanus — We shall meet in Babylon’ brought Alexander his death.
Calanus was a Hindu Naga Sadhu from Punjab, India. The ascetic belonged to the tribe of ‘gymnosophists’ i.e. naked wise men who regarded food and clothing as detrimental to the purity of thoughts. He self-immolated on the pyre, and the prophecy was his last word. The true meaning of Calanus’s words dawned on the Greeks much later.
From history to real-life situations:
We had a doyen in the neurology department who was whimsical but brilliant. Dr. Dalal has contributed chapters in the ‘Harrison’s Principles Of Medicine’ considered the Bible of all medical students. When he was a student, appearing for the final MD examination, the examiner — a clinician of great repute, was in for a surprise.
During practicals, a diagnosis has to be established after a thorough examination of a patient, and the management has to be discussed via a grilling inter-active viva session. A gentle reminder that this was in an era before the advent of neuro-imaging techniques like EMG, CT, and MRI scans. It was a test based on bedside skills — the holiest form of clinical experience.
Dr. Dalal’s diagnosis was Syringomyelia, a relatively rare neurological condition in which a cavity gets formed in the spinal cord. The examiner had no hesitation in accepting that but suggested he offer the differential diagnosis. Dr. Dalal replied, “With due respect Sir, I do not believe in DD. My working diagnosis is the final diagnosis.”
The examiner failed him because of his arrogance.
The terminal patient passed away in about six weeks, and an autopsy was performed, more out of academic curiosity. The histopathology report confirmed the diagnosis of Syringomyelia. The examiner, who was also the HOD, sent a handwritten note to Dr. Dalal to mark his attendance in the ensuing semester exam. The HOD wrote, “I will pass you with due honours without conducting the customary viva. I also appreciate your confidence and conviction”.
The anecdotal subject of DD, though hearsay, brought to light two great personalities. First, for the clinical acumen, and second, for the magnanimity. The two facets that make a great doctor i.e. competence and humanity.
