Murtagh’s Diagnostic Strategies (MDS) has been developed as an aide memoire and readily accessible reference to assist general practitioners to follow a clinical reasoning approach to patients’ common presenting problems.
This fail-safe diagnostic model encourages doctors to focus on the probability diagnosis and the differential diagnoses for the particular presenting problem, and also to consider life-threatening causative conditions that must not be missed. The strategy challenges doctors to consider certain subtle conditions called ‘masquerades’ that are worth checking if the diagnosis remains uncertain.
The strategy can be summarised with 5 questions that doctors should ask themselves:
What is the probability diagnosis?
What must not be missed?
What are common pitfalls for this problem?
Could the patient have one of the seven masquerades?
What is the patient trying to tell me (psychosocial issues)?
To test the hypothesis for the probability diagnosis, doctors need to consider the key features: key history, key examination and key investigations.
This key features approach aligns with what is expected of candidates for the Key Feature Problems (KFP) component of the Royal Australian College of General Practitioners (RACGP) Fellowship examination and other similar examinations.
MDS currently covers 100 of these common problems but the methodology can be used to diagnose many other presenting problems.
When a patient presents with a specific symptom the practitioner should make a provisional diagnosis from the clinical circumstances, including the age and other demographic features of the patient. The practitioner can then compare this hypothesis with the information for that symptom in MDS.
This is best illustrated by a case history:
Mrs KL, a 45-year-old housewife, presents with the problem of the recent onset of uncharacteristic hair loss. She has brought a plastic bag containing shed hair to the surgery. For the past three to four weeks her hair has been coming out in large clumps particularly when combing and washing.
After making a provisional diagnosis, refer to ‘Hair loss’ in MDS. You should arrive at the following key points.
Likely diagnoses (in order)
Alopecia areata (diffuse type)
Nature of hair loss onset—duration, quantity, rate of loss, diffuse or patchy
Characteristics of the hair such as scales, white bulbs
Precipitating factors—stress, fever, surgery, acute illness
Past history—skin disorders, cancer, thyroid disorders
Family history of hair loss
Drug history, especially cytotoxics, amphetamines, anti-epileptics, hormone agents, cessation OCP, other
General review—emphasis on examination of the scalp and endocrine system
Hair and scalp—look for exclamation mark hair, ‘white bulb’ hair, any bald patches and their nature, the unusual pattern of trichotillomania
Probably none—consider hair pull test, trichogram, FBE, TFTs
Footnote: KL had telogen effluvium precipitated by the emotional stress of a home burglary 4 months previous to the shedding of the hair (with white bulbs). Aided by support and counselling the hair loss ceased within months.
The RACGP Key Feature Problems exam
MDS is also an invaluable resource for doctors preparing for RACGP Fellowship exams. In the exam, a typical case provides a brief history of the presenting problem, then the following questions:
List the likely causes (differential diagnoses) — up to 3.
What other aspects of the history would you like to explore?
What are the appropriate investigations? List 2 to 4.
What are the important features of management? List 2 to 3.
Note: Doctors may be asked to select from a list of options, especially for the differential diagnoses and investigations.