Achieving an accurate diagnosis is crucial in reaching the goals of neurologic care: to alleviate signs and symptoms; to restore function; and to keep the patient in the best possible health. To achieve these goals, the doctor’s clinical reasoning must establish the correct hypotheses or differential diagnosis , arrive at the correct diagnosis, and initiate appropriate treatment. Studies have shown that errors in clinical reasoning are not rare. They usually stem from three factors: (1) inadequate basic science and medical disease knowledge; (2) incomplete and inaccurate data collection; and (3) incorrect integration and interpretation of the data collected. Acquisition of medical knowledge comes from reading medical articles, attending lectures, and experience from seeing many patients. Incomplete and inaccurate data collection may come from patient factors (poor historian, altered mental status, unavailable significant others for history, complex illness involving several organs, and multiple chronic illnesses with overlapping symptoms) or clinician factors (poor history taking skills with failure to ask key questions, poor listening to the patient’s answers, incomplete clinical exam, missing medical records, inaccurate laboratory data, and lack of appropriate laboratory tests). Incorrect integration and interpretation of data collected is complex and stems from ignoring key pieces or history, clinical or lab data, incorrect emphasis of pieces of the acquired data, failure to order key laboratory tests or neuroimaging, and failure to consider the correct differential diagnosis .

The expert clinician often is able to establish the correct diagnosis by listening to the history, forming key hypotheses, narrowing the hypotheses based on the neurologic exam , and ordering the key laboratory and neuroimaging tests. Forming the key hypotheses comes from clinical experience with pattern recognition, knowledge of the more likely (highest probability) diagnoses in that clinical situation, and the ability to order the appropriate tests to confirm the diagnosis. The challenge facing the medical student is to make an accurate diagnosis without the years of experience and extensive reading, which they do not possess at their level of education. Fortunately, there are methods to help a student narrow a differential diagnosis and increase their accuracy. The following eight steps in diagnosing neurologic conditions can be followed by a junior medical student to help them focus their diagnostic attention. This avoids costly mistakes due to ordering inappropriate laboratory tests, establishing an incorrect diagnosis, and prescribing the wrong treatment.