Syndromes

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The concept of a syndrome is important in medical care (and in epidemiology). A syndrome is a constellation of symptoms, possibly combined with risk factors and demographic characteristics of patients (e.g., age and gender). Familiar examples of syndromes are SARS (severe acute respiratory syndrome) and AIDS (acquired immune deficiency syndrome). A syndrome plays the same role as a diagnosis in medical careā€”it guides the physician in selection of treatments for patients.

In this chapter, we will be discussing syndromes such as respiratory that are far less diagnostically precise than SARS or AIDS. The syndromes used in automated analysis of chief complaints and ICD codes are diagnostically imprecise by intent. The developers of these syndromes recognize that chief complaints (and ICD-coded diagnoses obtained close to the time of admission) in general do not contain sufficient diagnostic information to classify a patient as having SARS or other more diagnostically precise syndrome. They create syndrome definitions that are sufficiently precise to be useful, but not so precise that few if any patients will be assigned to them automatically, based solely on information contained in a four- or five-word chief complaint (or ICD code assigned early during the process of medical care).

Table 23.2 is the set of syndromes used by the RODS system. The table shows each syndrome name (which is just a convenient handle to reference the syndrome definition) and its definition. The RODS system uses the syndrome definitions in two ways. First, it makes them available to epidemiologists and other users of the system to assist in interpreting time series and maps of chief complaint data that have been aggregated by syndrome. If the user sees an increase in a syndrome such as respiratory, his interpretation of the increase should be that it could be due to any disease that is consistent with the definition of the respiratory syndrome. Second, RODS provides the definitions to individuals who are developing training sets (discussed in Chapter 17) for the CoCo parser.3

Tables 23.3 and 23.4 are syndrome classification systems used by Maryland Department of Hygiene and Mental Health and the New York City Department of Health and Mental Hygiene, respectively.

A final subtle point about the definition of syndromes that applies to both chief complaint syndrome definitions and ICD-code sets described later: The field of artificial intelligence distinguishes between intensional and extensional definitions. Tables 23.2 and 23.4 are intensional definition of syndrome categories. They express the intent of the system designer.

3 In practice, we train the CoCo parser using a set of approximately 10,000 chief complaints that a human has manually classified into one of these eight categories. Note that there is nothing domain specific about a Bayesian classifier as it is a mathematical formalism. CoCo could just as easily be trained to recognize a set of injury-related chief complaints.

table 2 3.2 CoCo Syndrome Definitions

CoCo Syndrome

Definition

Gastrointestinal Includes pain or cramps anywhere in the abdomen, nausea vomiting, diarrhea and abdominal distension or swelling.

Constitutional Is made up of nonlocalized, systemic problems including fever, chills, body aches, flu symptoms (viral syndrome), weakness, fatigue, anorexia, malaise, irritability, weight loss, lethargy, sweating (diaphoresis), light headedness, faintness and fussiness. Shaking (not chills) is not constitutional but is other. Includes all of the "vaguely unwell" terms: doesn't feel well, feels ill, feeling sick or sick feeling, feels bad all over, not feeling right, sick, in pain, poor vital signs.

Shaking or shaky or trembling (not chills) are not constitutional but are other (8).

However, tremor(s) is neurological (7).

Note: cold usually means a URI (cold symptoms; 3), not chills. Weakness, especially localized, is often neurological (7), rather than constitutional.

Respiratory Includes the nose (coryza) and throat (pharyngitis), as well as the lungs. Examples of respiratory include congestion, sore throat, tonsillitis, sinusitis, cold symptoms, bronchitis, cough, shortness of breath, asthma, chronic obstructive pulmonary disease (COPD), pneumonia, hoarseness, aspiration, throat swelling, pulmonary edema (by itself; if combined with congestive heart failure, it is 8). If both cold symptoms and flu symptoms are present, the syndrome is respiratory.

Note: "Sore throat trouble swallowing" is respiratory, not respiratory and botulinic. That is, the difficulty in swallowing is assumed to be an aspect of the sore throat.

Rash Includes any description of a rash, such as macular, papular, vesicular, petechial, purpuric or hives. Ulcerations are not normally considered a rash unless consistent with cutaneous anthrax (an ulcer with a black eschar).

Note: Itch or itchy by itself is not a rash.

Hemorrhagic Is bleeding from any site except the central nervous system, e.g., vomiting blood (hematemesis), nose bleed (epistaxis), hematuria, gastrointestinal bleeding (site unspecified), rectal bleeding and vaginal bleeding. Bleeding from a site for which we have a syndrome should be classified as hemorrhagic and as the relevant syndrome (e.g., Hematochesia is gastrointestinal and hemorrhagic; hemoptysis is respiratory and hemorrhagic). Bleeding from a site for which we have a syndrome should be classified as hemorrhagic only without reference to the relevant syndrome, except hematochesia... hemoptysis.

Note: "Spitting up blood" is assumed to be hemoptysis.

Botulinic Includes ocular abnormalities (diplopia, blurred vision, photophobia), difficulty speaking (dysphonia, dysarthria, slurred speech) and difficulty swallowing (dysphagia).

Neurological Covers nonpsychiatric complaints which relate to brain function. Included are headache, head pain, migraine, facial pain or numbness, seizure, tremor, convulsion, loss of consciousness, syncope, fainting, ataxia, confusion, disorientation, altered mental status, vertigo, concussion, meningitis, stiff neck, tingling, numbness, cerebrovascular accident (CVA; cerebral bleed), tremor(s), vision loss or blindness (but changed or blurred vision or vision problem is botulinic). Dizziness is constitutional and neurological.

Note: headache can be constitutional is some contexts, for example, "headache cold sxs achey" or "headache flu sxs "

Other Is a pain or process in a system or area we are not monitoring. For example, flank pain most likely arises from the genitourinary system, which we are not modeling, and would be considered other. Chest pain with no mention of the source of the pain is considered other (e.g., chest pain [other] versus pleuritic chest pain [respiratory]). Earache or ear pain is other. Trauma is other. Hepatic encephalopathy (not neurological), dehydration (not constitutional), difficulty sleeping or inability to sleep (not constitutional), constipation (not constitutional), and choking (but aspiration is respiratory) are all other.

Note: A physician or other medical expert refers to these definitions when creating training examples for the CoCo Bayesian classifier (described in Chapter 17).

The extensional definition of each syndrome is the actual set of chief complaints that NLP parsers, trained or configured based on the intensional definitions, assign to the categories.

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