Because GPs must be able to distinguish rare, life (or lifestyle) threatening conditions from more common conditions, it is essential to have a diagnostic framework that accomplishes this efficiently. This framework must be sensitive enough not to miss these major conditions, but specific enough to ensure that patients and the community are not subjected to unnecessary, expensive investigations and inconvenience. It needs to identify the patient's concerns and possible psychosocial basis for presentation of physical symptoms. Such a framework has been developed by Murtagh . It directs the practitioner to ask five questions when confronted with a clinical problem.
1. What is the probability diagnosis?
2. What serious disorders must not be missed?
3. What disorders are commonly missed?
4. Is this one of the masqueraders1 in medical practice?
5. Is this patient trying to tell me something?
The probability diagnosis is that condition most likely to explain the presenting complaint. It highlights the relationship between the prevalence of a condition and the likelihood that the condition is truly present. A symptom or sign reflective of a high prevalence condition will most likely be due to that complaint. A symptom reflective of a rare condition is much more likely to be a false-positive finding. Since
'The masqueraders can be grouped into primary and secondary groups. The primary (most common) masqueraders are: depression, diabetes mellitus, drugs, anemia, thyroid disease, spinal dysfunction, and urinary tract infection. A secondary (less common) list includes: chronic renal failure, HIV/AIDS, rare bacterial infections (e.g. subacute bacterial endocarditis, tuberculosis), systemic viral infections (e.g. infectious mononucleosis, hepatitis A, B, C, D, E), neurological dilemmas (e.g. Parkinson's disease, multiple sclerosis), connective tissue disorders (e.g. systemic lupus erythe-matosus, polymyalgia rheumatica).
GPs work in the community, they are familiar with what is common in that community. By expecting the common, they will rarely be mistaken.
However, they must not miss the rare but serious causes of a symptom. This may mean testing a little more intensely to rule out the condition, or having a strategy that identifies the rare and important as its true identity declares itself over time (see below).
Some causes of a condition are commonly misdiagnosed, and should be considered. An example is constipation as a cause of a child's abdominal pain. There are also symptom complexes that present in a variety of nonspecific ways that can be missed if not considered. These are the masqueraders. An example is hypothy-roidism, which can present as depression, dementia, weight gain, tiredness, hoarse voice, or even cardiac failure.
Finally, it is a common occurrence that physical symptoms can be the presenting symptoms of psychosocial or spiritual distress. If the pattern of illness does not ring true, or if there is dissonance between the described severity and objective signs and symptoms, the GP is alerted to the presence of potential personal distress.
A great strength of general practice is the longitudinal care of patients, which allows both the opportunity to develop a comprehensive picture of the patient's social context, and opportunities to observe the natural history of disease. This creates opportunities to add a "safety net" to the diagnostic process. Many of the conditions that GPs see have differing time disease trajectories, but present with markedly similar conditions in the early stages. Because primary practice allows for repeated visits, the "return visit" becomes a powerful diagnostic tool. The clinical picture becomes clearer as time progresses. Conditions with a steady progression of symptoms with time can be distinguished from ones that are self-limiting, simply by a review in a week or a month. It is much more difficult to put in place such a means of review in secondary or tertiary care facilities, due to organizational, manpower, and funding constraints.
It is in this context that problems in identifying and managing cancer of the thyroid in general practice become obvious.
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