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A. Hypothesis testing and reaching a provisional diagnosis
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When the history suggests neurologic disease, the NE must include the critical tests for the integrity of neural structures that the lesion or disease could affect. The goal is to achieve the best provisional diagnosis. To reach a provisional diagnosis, the Ex poses and tests numerous diagnostic hypotheses during the history, physical examination, and, later, the laboratory work-up. The thinking process is one of posing if's: "If the Pt has such and such a disease or sign, then I should also find so and so. Very well, I will look for that next."
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B. The concept of closure (cloture)
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After the history, after the examination, and after the hypothesizing, the next event in the medical process is the cloture. Cloture is a technical term meaning, now that the arguments have been heard and the data presented, the time has come to pose the critical question(s) for decision and action. The provisional diagnosis and the differential diagnosis derived from it are the outcomes of the cloture, and the medical management is the action (Figure 15–1).
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C. The diagnostic catechism
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The cloture requires six questions, three primary and the three derivative, that form the diagnostic catechism (Table 15–3).
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D. Is there a lesion (Table 15–3, question 1)?
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The first dichotomy is whether the disorder is organic or psychogenic. That is the meaning of the first question, "Is there a lesion or a disease?" The Ex initially tries to discover neurologic signs that identify an anatomic lesion. Then the Ex considers organic disorders with biochemical lesions, such as some types of epilepsy or migraine, that exhibit no physical signs in the interictal examination. Next, the Ex considers emotional disorders with no lesion. The Ex must try to separate psychogenic from organic disorders because the provisional diagnosis thus achieved determines the extent and type of clinical and laboratory tests required to establish the final diagnosis. To answer yes to the question, "Is there a lesion?" the Ex hopes to find at least one sign. One firm sign may mean more than a multitude of symptoms. In answering the question, think through Figure 15–2 to start generating the possibilities in your mind.
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E. Where is the lesion or the disease (Table 15–3, question 2)?
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If the clinical evidence suggests a lesion or disease, ask these questions:
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Is the lesion or disease in the structure or the biochemistry of the Pt?
Is it at the level of gene, chromosome, or cell? Is it at the level of blending of cells into tissues or of tissues into organs, or of organs into systems, or of systems into the general somatotype of the Pt? Do the findings constitute a diagnostic neuroanatomic, morphologic, biochemical, or genetic syndrome?
Can a decision be made as to the organ or organs, system or systems involved by the lesion? If it affects the nervous system, is the lesion:
In the PNS or CNS?
If the lesion involves the CNS, is it intra-axial or extra-axial?
If intra-axial, is it focal: in the cerebrum, ventricular cavities or passageways, basal ganglia, brainstem, cerebellum, or spinal cord; or is it multifocal or diffuse?
If the lesion could be extra-axial, is it:
In a meningeal or bony covering?
In a meningeal space: epidural, subdural, or subarachnoid?
In a nerve root, plexus, peripheral nerve, neuromuscular junction, or muscle?
When the Pt's symptoms and signs suggest a neurologic disease, try to classify it as motor, sensory, sensorimotor, headache, or organic mental syndrome.
If motor, think through Figure 15–3 to locate the neuronal system affected; if an involuntary movement syndrome, see Figure 15–4.
If sensory, see Figure 15–5.
If a headache, see Figure 15–6.
If an organic mental syndrome, see Figure 15–7.
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F. What is the lesion or the disease (Table 15–3, question 3)?
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Having hypothesized the neuronal system, or systems, involved, and the lesion site, the Ex next has to hypothesize what the lesion is. For this purpose, systematically think through the entities shown in Figure 15–8. Then state a provisional diagnosis according to the principle of parsimony: the simplest diagnosis that will explain the signs and symptoms.
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G. What is the optimum diagnostic management (Table 15–3, question 4)?
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What tests, clinical or laboratory, will confirm or reject the provisional diagnosis and establish the final diagnosis?
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The explicitly stated provisional diagnosis provides the basis to generate a differential diagnosis list. The Ex selects any further clinical tests that will best affirm or deny the provisional diagnosis or point to another diagnosis. Having exhausted all clinical tests, the Ex selects laboratory tests according to these principles:
Select the one or two best tests to support or reject the provisional diagnosis.
Given tests of approximately equal clinical value, select the simplest, safest, and cheapest ones, but never curtail the investigation in the sole interest of "cost containment." Failure to diagnose a diagnosable disease is the costliest mistake of all.
When faced with a hopeless or untreatable disorder, take all reasonable steps to exclude a treatable disorder.
To select the most appropriate laboratory tests, review the possible ones listed in Table 13–1.
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H. What is the optimum therapeutic management (Table 15–3, question 5)?
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State the therapeutic goals and how to meet them. Just what can you hope to do for the Pt?
What emotional, educational, or socioeconomic perils does the Pt face because of the illness? What agencies—lay, rehabilitative, vocational, or governmental—might help?
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I. What is the optimum preventative management (Table 15–3, question 6)?
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Having identified the Pt's illness, the Ex has to identify other persons at risk. How can they be reached and offered prophylaxis? Consider for Pts with environmentally induced, contagious or infectious, or hereditary diseases.
Follow the Pt to ensure that your final diagnosis is indeed final and that the Pt's subsequent course continues to confirm its finality.