The immune system functions as the body’s dedicated defense force, distinguishing between foreign invaders and the body’s own healthy cells. An autoimmune disease occurs when this mechanism malfunctions, causing the immune system to mistakenly target and attack the body’s own tissues. With over 100 different known autoimmune conditions, such as rheumatoid arthritis and Type 1 diabetes, these disorders represent a significant global health challenge. Given the complexity of the immune system, a common question is whether a person can develop more than one of these conditions.
The Reality of Polyautoimmunity
The answer to whether one can have multiple autoimmune diseases is yes; this co-occurrence is a recognized clinical phenomenon. When a person is diagnosed with two distinct autoimmune conditions, it is referred to as polyautoimmunity. Having three or more confirmed autoimmune diseases is classified as Multiple Autoimmune Syndrome (MAS).
For individuals already living with one autoimmune disorder, the likelihood of developing another is statistically elevated. Studies indicate that approximately 25% of patients diagnosed with one autoimmune disease are at risk of developing an additional one. In some patient cohorts, the prevalence of polyautoimmunity is even higher, with one report finding that 34.4% of patients with an autoimmune disease had at least a second one.
This clustering often follows recognizable patterns, suggesting underlying connections between certain diseases. Common pairings include rheumatoid arthritis (RA) and Sjögren’s syndrome, or systemic lupus erythematosus (SLE) co-occurring with Sjögren’s syndrome. Endocrine-related diseases also frequently pair, such as Type 1 diabetes and autoimmune thyroid conditions like Hashimoto’s or Graves’ disease. For example, one large-scale study found that 16.1% of patients with Graves’ disease went on to develop another autoimmune disorder.
There is no absolute limit to the number of autoimmune diseases a person can develop, though the co-occurrence of five or more conditions is considered extremely rare. The risk of developing a second or third condition is notably higher because the underlying immune dysregulation is already present, making the body more susceptible to further self-directed attacks.
Shared Biological Drivers of Multiple Conditions
The development of multiple autoimmune diseases in one individual is not a random event; it is driven by several shared biological mechanisms that predispose the body to generalized immune system errors. One primary factor is shared genetic susceptibility, particularly involving the genes of the Major Histocompatibility Complex (MHC), also known as the Human Leukocyte Antigen (HLA) system. These genes produce proteins that help immune cells distinguish between “self” and “non-self.”
Certain HLA alleles increase the general predisposition to autoimmunity rather than conferring risk for a single disease. For instance, the HLA-DRB1\03:01 allele is associated with an increased risk for systemic lupus erythematosus, Sjögren’s syndrome, and Type 1 diabetes. This suggests the genetic blueprint creates a less-stable immune environment, making individuals vulnerable to multiple self-targeting attacks.
Environmental triggers, such as viral infections, can also act as a spark for a systemic autoimmune response. A single significant infection may initiate a cascade of immune activation that affects multiple tissues or organs simultaneously in a genetically susceptible person. Viruses like the Epstein-Barr virus have been implicated as potential environmental factors that may trigger the onset of autoimmunity.
A third crucial mechanism is known as epitope spreading. An autoimmune response begins when the immune system targets a specific small piece of a protein, called an epitope, on a particular tissue. As the initial attack causes tissue damage, various cellular proteins and their epitopes are released into the body. The immune system may then broaden its attack to include these newly exposed epitopes, even if they are on different proteins or in different tissues. This expansion of the immune response beyond the initial target can effectively spread the autoimmune attack to other areas of the body, leading to a second or third diagnosis.
The Complexities of Diagnosis and Management
The practical reality of having multiple autoimmune diseases presents significant challenges for both patients and healthcare providers. One of the most common difficulties is diagnostic delay, as the symptoms of different conditions can overlap or mask one another. For example, the fatigue and joint pain characteristic of one disease may be mistakenly attributed to a pre-existing condition, prolonging the patient’s diagnostic journey.
Patients with autoimmune conditions often spend an extended period seeking a definitive diagnosis, with some statistics reporting an average diagnostic delay of over four years and multiple physician visits. This complexity is compounded when symptoms are intermittent, with periods of flare-ups and remission that can confuse the clinical picture. Because many symptoms like joint pain or rash can be linked to several different conditions, a lack of specific diagnostic tests for many autoimmune disorders necessitates a detailed combination of clinical evaluation and lab results.
Management of polyautoimmunity requires a careful balancing act, as treatments for one disease may affect another. Many autoimmune conditions are treated with immunosuppressive medications to dampen the overactive immune response. However, using these powerful drugs increases the risk of side effects, such as infections or the potential for drug interactions when multiple medications are required.
In some instances, a treatment designed for one condition, like a specific biologic drug, may inadvertently trigger a different autoimmune syndrome in a susceptible patient. Therefore, care must be highly coordinated, often involving multiple specialists who must communicate effectively to manage the systemic impact of these chronic conditions. This integrated approach is necessary to maintain the patient’s quality of life and optimize their long-term health outcomes.