As Populations Age, Occam’s Razor Loses Its Diagnostic Edge

The principle of parsimony, often referred to as “Occam’s razor,” favors a unifying explanation over multiple ones, as long as both explain the data equally well. This heuristic, widely used in medical practice, advocates for simpler explanations rather than complex theories. However, its application in modern medicine has sparked debate.

“Hickam’s dictum,” a counterargument to Occam’s razor, asserts that patients — especially as populations grow older and more fragile — can simultaneously have multiple, unrelated diagnoses. These contrasting perspectives on clinical reasoning, balancing diagnostic simplicity and complexity, are both used in daily medical practice.

But are these two axioms truly in conflict, or is this a false dichotomy?

Occam’s Razor and Simple Diagnoses

Interpersonal variability in diagnostic approaches, shaped by the subjective nature of many judgments, complicates the formal evaluation of diagnostic parsimony (Occam’s razor). Indirect evidence suggests that prioritizing simplicity in diagnosis can result in under-detection of secondary conditions, particularly in patients with chronic illnesses.

For example, older patients with a known chronic illness were found to have a 30%-60% lower likelihood of being treated for an unrelated secondary diagnosis than matched peers without the chronic condition. Other studies indicate that a readily available, simple diagnosis can lead clinicians to prematurely close their diagnostic reasoning, overlooking other significant illnesses.

Beyond Hickam’s Dictum and Occam’s Razor

A recent study explored the phenomenon of multiple diagnoses by examining the supposed conflict between Hickam’s dictum and Occam’s razor, as well as the ambiguities in how they are interpreted and used by physicians in clinical reasoning.

• Part 1: Researchers identified articles on PubMed related to Hickam’s dictum or conflicting with Occam’s razor, categorizing instances into four models of Hickam’s dictum:
  1. Incidentaloma: An asymptomatic condition discovered accidentally.
  2. Preexisting diagnosis: A known condition in the patient’s medical history.
  3. Causally related disease: A complication, association, epiphenomenon, or underlying cause connected to the primary diagnosis.
  4. Coincidental and independent disease: A symptomatic condition unrelated to the primary diagnosis.
• Part 2: Researchers analyzed 220 case records from Massachusetts General Hospital, Boston, and clinical problem-solving reports published in The New England Journal of Medicine between 2017 and 2023. They found no cases where the final diagnosis was not a unifying one.
• Part 3: In an online survey of 265 physicians, 79% identified coincidental symptomatic conditions (category 4) as the least likely type of multiple diagnoses. Preexisting conditions (category 2) emerged as the most common, reflecting the tendency to add new diagnoses to a patient’s existing health profile. Almost one third of instances referencing Hickam’s dictum or violations of Occam’s razor fell into category 2.

Causally related diseases (category 3) were probabilistically dependent, meaning that the presence of one condition increased the likelihood of the other, based on the strength (often unknown) of the causal relationship.

Practical Insights

The significant finding of this work was that multiple diagnoses occur in predictable patterns, informed by causal connections between conditions, symptom onset timing, and likelihood. The principle of common causation supports the search for a unifying diagnosis for coincidental symptoms. It is not surprising that causally related phenomena often co-occur, as reflected by the fact that 40% of multiple diagnoses in the study’s first part were causally linked.

Thus, understanding multiple diagnoses goes beyond Hickam’s dictum and Occam’s razor. It requires not only identifying diseases but also examining their causal relationships and the timing of symptom onset. A unifying diagnosis is not equivalent to a single diagnosis; rather, it represents a causal pathway linking underlying pathologic changes to acute presentations.

This story was translated from Univadis Italy using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.