The concept of a combined underlying disease
In medical practice, situations sometimes arise when an autopsy reveals several diseases at once, each of which played a role in thanatogenesis, and it is impossible to choose a single cause of death. In such cases, physicians use categories of combined pathology.
In modern practice, the term "combined underlying disease" is rarely encountered. The pathologoanatomical diagnosis immediately indicates the specific type of relationship between the pathologies: competing or combined processes.
Competing diseases and their formatting
Competing diseases are understood as two or more processes, each of which is capable of independently leading to a fatal outcome.
- Clinical example: An elderly patient with stage IV gastric cancer and severe coronary artery atherosclerosis. The tumor causes hypercoagulability leading to thrombosis and myocardial infarction.
- Diagnosis logic: The tumor was already fatal, but the developed infarction also became a fatal cause. Competition arises between two fatal nosologies.
When formulating the diagnosis, the first pathology is recorded under the heading "Underlying combined disease", and the second as a "Competing disease".
Combined diseases
Combined diseases are those with different etiologies and mechanisms of development, while each of them individually is not fatal. They coincide in time, mutually aggravate the course of each other, and together lead to the death of the organism.
An example is a clinical situation where a female patient, following osteosynthesis of a femoral neck fracture, developed bilateral pneumonia due to bed rest. The fracture in isolation does not cause instant death, and pneumonia is not a direct complication of the trauma, as with good care it might not have occurred. Both processes proceed in parallel, so this condition is classified as a combined underlying disease.
Background disease and polypathies
A background disease is a pathology that played a key role in the origin and severe course of the main process, contributing to fatal complications. A historical example is myocardial infarction and strokes: pathogenetically they are complications of atherosclerosis or hypertensive disease, but for the sake of correct WHO statistics, they are elevated to the underlying disease, while the causes are sent to the background.
Polypathies represent a group of underlying diseases that may be formatted as a family of related diseases or a random association. They include combinations of competing, combined, or background processes, where the nosology that directly led to the fatal outcome is recognized as the main cause of death.
Briefly: answers to topical questions
What are the ICD coding rules for combined underlying diseases?
In the ICD system, the cause of death is coded exclusively by the underlying disease. If several diseases (polypathies) are present, including competing, combined, or background pathologies, the following selection principles for coding are applied:
- Selection of nosology — the disease that became the direct cause of death is taken as the underlying disease.
- Coding of the cause of death — is carried out precisely according to the chosen underlying disease in the ICD system.
The category "combined underlying disease" itself is rarely used in modern practice; the type of relationship between the diseases is usually indicated directly in the diagnosis.
Competing means they fight for primacy (each is fatal on its own). Combined means they act as a team (not fatal individually, but destroy together). Background is the soil on which everything grew.
Class and exam questions
How do competing diseases differ from combined diseases?
Competing diseases are each fatal on their own. Combined diseases would not lead to death individually, but due to simultaneous development and mutual aggravation, they destroy the organism together.
Why is myocardial infarction elevated to the underlying disease in the presence of atherosclerosis?
Pathogenetically, an infarction is a complication of atherosclerosis or hypertensive disease, but by decision of the WHO, for accurate medical statistics, it is formatted as the underlying disease, and atherosclerosis is indicated as a background disease.
Can pneumonia following a femoral neck fracture be considered a complication of this fracture?
No, there is no direct pathogenetic link between them, since with adequate care pneumonia might not have developed. It is considered a combined disease.
What else to study on this topic
- History and World Health Organization standards for recording myocardial infarction
- Features of thanatogenesis in the combination of trauma and infectious complications
- Rules for constructing a pathologoanatomical diagnosis in polypathies
- Criteria for distinguishing disease families from random associations
- The role of background nosologies in the development of cerebrovascular accidents
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