“Always listen to the patient. They might be telling you the diagnosis.” – Sir William Osler

Doctors rely on both signs and symptoms to make a diagnosis. Signs are objective observations—measurements, like heart rate or blood pressure, or a doctor’s assessments, like the presence of a rash. Symptoms, by contrast, are the subjective expression of what a patient feels, like tiredness, itchiness, or pain. A doctor assesses signs herself; for symptoms, she relies on report of her patient.

Symptoms are discovered through the patient history. Gathering a patient’s history is quite often the starting point of the diagnostic process, making certain diagnoses more likely, ruling others out, and prompting a further course of evaluation. The history allows for a detailed account of symptoms, including their onset, intensity, and alleviating factors.

A history is usually presented by the patient and is therefore largely subjective. That is, it consists of the patient’s personal account and interpretation of his own experiences. For example, if a patient tells a doctor he’s been feeling stressed for the past month after a traumatic event, this is a subjective self-report that the doctor will generally take at face value.

Sometimes, there is no clear interpretation of a symptom. If a patient says she believes that aliens are sending beams to control her actions, the psychiatrist is likely to say this person has delusional thought content. (The account may be aided by evidence she has covered her house in aluminum foil in an attempt to stop the beams.) However, the psychiatrist’s assessment of delusions is less reliable if a patient worries his spouse is cheating on him. Is he psychotic and delusional? Maybe he is naturally mistrusting. Maybe he’s simply misinterpreting unrelated events. Or maybe his beliefs are true.

Objective measures

In a psychiatric exam, it’s often the case that a history alone is sufficient to allow the psychiatrist to determine a patient’s condition.^[1] However, just as in other fields of medicine, there are also objective, observable signs regarding the patient’s mental condition.

For example, someone who suffers from auditory hallucinations (i.e., “hears voices”) might be witnessed speaking to themselves or constantly looking around the room as if trying to hear something. People with depression may appear despondent, poorly groomed, or tearful. Problems with thought process may be objectively noted through a patient’s errors in syntax, grammar, or logic. Physiological measurements factor in as well: an increased respiratory and heart rate may indeed provide evidence of a panic attack.

Forensic methods

In a clinical setting, the distinction between objective signs and subjective symptoms is important only insofar as it helps the psychiatrist understand and treat the patient’s suffering. Even if a patient gives a biased or incomplete report, it can still be useful in helping them feel better.

Courts, however, have different goals. Objectivity is a requirement when making decisions in the name of justice. Though a subjective history remains essential in legal settings, there are two important ways to improve assessment validity and diagnostic accuracy beyond patient self-report.

First, the forensic psychiatrist must ensure that the history provided is complete. The psychiatrist must studiously document a patient’s symptoms, their frequency, their intensity, their duration, their onset, their course over time, and their exacerbating and alleviating factors. For legal evaluations, this may often require asking uncomfortable questions or gathering much more detail than typical for a normal clinical visit (in which it is assumed that a complete understanding of the patient’s mental health will emerge through subsequent visits).

Second, the forensic psychiatrist augments a self-report with collateral information, obtained from sources other than the patient herself.

In a clinical setting, there are some situations where a psychiatrist will reach out to a patient’s acquaintances for more information. Use of collateral informants is considered the standard of care, for example, in emergency-room assessments of suicide risk, violence risk, or grave disability.

Collateral information can come from family members, romantic partners, or anyone else who knows the patient well and can speak to changes in mood, behavior, or energy levels. They can corroborate symptoms (for example, an informant who notices the patient screaming for help in his sleep may educate the physician’s understanding of the severity of the patient’s nightmares). Or they may have insight into medication compliance and effectiveness. Collateral information may also include reports from other doctors, nurses, and technicians.

In a legal setting, there is even more collateral information available. An employee’s performance reviews provide information about how he functions at work. Report cards may suggest recent changes at school. Witness and police reports provide observations about behavior that may not be directly observable by the psychiatrist in a personal evaluation. Prior medical records can include data on one’s mental status. And, more recently, social media posts and other online activity have become valuable tools for understanding a person’s mental state.

With this extra detail, a forensic psychiatrist can issue a more precise diagnosis as required to answer various legal questions, often with enormous ramifications. This, then, is the essential challenge to the forensic psychiatrist: focus on the details enough to meet the rigorous evidentiary standards of the court—all the while still heeding Dr. Osler’s sage advice.