Systemic Lupus Erythematosus (SLE), commonly known as lupus, is a systemic autoimmune disorder where the immune system mistakenly attacks its own tissues and organs, causing widespread inflammation and damage throughout the body. Autoimmune Thyroid Disease (AITD) primarily targets the thyroid gland, resulting in conditions like Hashimoto’s thyroiditis (hypothyroidism) or Graves’ disease (hyperthyroidism). Both disorders share non-specific symptoms and systemic effects, making confusion between lupus and AITD a common diagnostic challenge. This overlap frequently leads practitioners to initially suspect one condition when the other is present, or to overlook the presence of both.
Symptom Overlap
Both lupus and AITD present with diffuse, non-specific symptoms that make initial differentiation difficult. The most frequently reported overlapping complaint is profound, unexplained fatigue that is not alleviated by rest. This tiredness stems from chronic inflammation in lupus or metabolic dysregulation in AITD, particularly hypothyroidism.
Generalized muscle and joint pain (arthralgia) is a significant point of confusion, being a hallmark of lupus flares and a common symptom of untreated hypothyroidism. Patients may also experience hair loss and mood disturbances, such as anxiety, depression, and difficulty with concentration (“brain fog”). These symptoms reflect the systemic impact of chronic illness.
The shared nature of these complaints means diagnosis cannot rely on symptoms alone. A patient could be experiencing lupus, Hashimoto’s thyroiditis, or a combination of the two, requiring specific laboratory investigation.
Distinguishing Diagnostic Markers
Lupus Markers
Distinguishing between lupus and AITD relies heavily on specific blood tests that identify the unique autoantibodies produced in each condition. For lupus, the Antinuclear Antibody (ANA) test is a foundational screening tool, indicating the presence of autoantibodies targeting the cell’s nucleus. While a positive ANA is nearly universal in lupus, it is not specific, as it can also be found in a significant percentage of people with Hashimoto’s or Graves’ disease.
To confirm a lupus diagnosis, clinicians look for more specific markers, particularly anti-double-stranded DNA (anti-dsDNA) and anti-Smith (anti-Sm) antibodies. The presence of these specific antibodies, alongside clinical symptoms, provides strong evidence for lupus rather than a thyroid-only disorder. Lupus diagnosis is also supported by non-specific inflammatory markers like an elevated erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP).
AITD Markers
For autoimmune thyroid disease, the diagnostic focus is on evaluating thyroid function and identifying specific thyroid autoantibodies. The primary test is Thyroid Stimulating Hormone (TSH), which is typically elevated in hypothyroidism (Hashimoto’s) and suppressed in hyperthyroidism (Graves’ disease). This is usually checked alongside Free T4 levels, which measure the amount of active thyroid hormone in the blood.
The presence of specific antibodies directed against the thyroid gland confirms the autoimmune nature of the disorder. Specific antibodies for AITD include:
- Anti-Thyroid Peroxidase (anti-TPO) and anti-Thyroglobulin (anti-Tg) antibodies, characteristic of Hashimoto’s thyroiditis.
- TSH Receptor Antibodies (TRAb), which identify Graves’ disease by stimulating the thyroid gland.
The Shared Autoimmune Mechanism
The confusion between lupus and AITD is rooted in the fact that both are fundamentally autoimmune disorders, sharing common underlying biological pathways. Autoimmunity involves the immune system losing tolerance and attacking healthy tissues, leading to the production of autoantibodies and chronic inflammation in both conditions.
Lupus is classified as a systemic autoimmune disease because the immune response targets many different organs simultaneously. In contrast, Hashimoto’s and Graves’ are organ-specific autoimmune diseases, focused primarily on the thyroid gland. Despite this distinction, both share genetic risk factors and involve similar patterns of immune cell activation and inflammatory signaling molecules (cytokines).
This shared foundation explains why a person predisposed to one autoimmune condition is more likely to develop another. The chronic systemic inflammation characterizing lupus can also contribute to the development of thyroid dysfunction.
When Both Conditions Occur Together
While misdiagnosis is possible due to symptom overlap, a more common scenario is the coexistence of both conditions, known as polyautoimmunity. Individuals diagnosed with lupus have a significantly increased risk of developing a second autoimmune condition, particularly AITD, which is one of the most frequent comorbidities observed.
Studies indicate that the prevalence of AITD, especially Hashimoto’s thyroiditis leading to hypothyroidism, is much higher in the lupus population than in the general population, with estimates ranging from 20% to 45%. Given this heightened risk, it is standard practice for clinicians managing lupus to regularly screen for concurrent AITD.
The presence of thyroid autoantibodies can even precede the onset of clinical thyroid dysfunction in lupus patients, highlighting the need for proactive monitoring, even if symptoms are initially attributed to lupus.