Lupus is a chronic autoimmune disease where the immune system mistakenly attacks healthy tissues and organs. This can lead to inflammation and damage in various areas, such as joints, skin, kidneys, brain, heart, and lungs. Its wide array of symptoms and variable presentation make diagnosis challenging, often leading to confusion with other conditions. Understanding these mimicking diseases is important.
Why Overlapping Symptoms Occur
In autoimmune diseases, the immune system malfunctions, targeting the body’s own healthy cells and tissues. This misdirected attack often results in widespread inflammation, which can manifest similarly across different conditions.
Many autoimmune diseases, including lupus, can affect similar organ systems. Joint pain, fatigue, and skin rashes are common manifestations of systemic inflammation, regardless of the specific autoimmune condition. The body’s general inflammatory response to an immune system attack can produce a range of symptoms, making it difficult to pinpoint a precise diagnosis based on symptoms alone.
Autoimmune Conditions That Mimic Lupus
Several autoimmune conditions present with symptoms that frequently overlap with lupus, requiring careful differentiation.
Rheumatoid arthritis (RA) causes chronic joint inflammation, leading to pain, stiffness, and swelling, often in the small joints of the hands and feet. While both RA and lupus can cause joint pain and stiffness, RA more commonly results in noticeable joint swelling and can lead to joint deformity and bone erosion, which is less typical in lupus. Diagnostic tests for RA often reveal rheumatoid factor or anti-citrullinated protein antibody (ACPA), markers less specific or absent in lupus.
Sjögren’s syndrome primarily targets moisture-producing glands, leading to prominent dry eyes and dry mouth. Like lupus, it can also cause fatigue, joint pain, and skin rashes. However, the severity of dryness is a distinguishing feature in Sjögren’s. Specific antibodies, such as anti-Ro/SSA and anti-La/SSB, are more strongly associated with Sjögren’s, though they can sometimes be present in lupus.
Systemic sclerosis, also known as scleroderma, involves the hardening and tightening of the skin and connective tissues. Shared symptoms with lupus include fatigue, joint pain, and Raynaud’s phenomenon (fingers and toes turning white or blue in response to cold or stress). The characteristic skin thickening and specific autoantibodies, like anti-centromere or anti-Scl-70, help differentiate scleroderma from lupus.
Mixed connective tissue disease (MCTD) is considered an overlap syndrome, displaying features of lupus, systemic sclerosis, and polymyositis (muscle inflammation). Individuals with MCTD often experience Raynaud’s phenomenon, swollen hands, and muscle weakness alongside general fatigue and joint pain. A key distinguishing laboratory marker for MCTD is a high concentration of anti-U1-RNP (ribonucleoprotein) antibodies, which are highly specific to this condition.
Drug-induced lupus is a temporary condition caused by certain medications, such as procainamide, hydralazine, and minocycline. Its symptoms mimic those of systemic lupus, including muscle and joint pain, fever, and fatigue. Unlike systemic lupus, it rarely affects major organs like the kidneys or brain. Symptoms typically resolve within six months after discontinuing the medication, and anti-histone antibodies are frequently present.
Non-Autoimmune Conditions with Similar Symptoms
Beyond autoimmune conditions, some non-autoimmune diseases also present with symptoms that frequently overlap with lupus, leading to diagnostic challenges.
Fibromyalgia is a chronic pain disorder characterized by widespread musculoskeletal pain, fatigue, sleep disturbances, and cognitive difficulties (“fibro fog”). While both fibromyalgia and lupus cause fatigue and body aches, fibromyalgia does not involve the inflammation, specific autoantibodies, or organ damage seen in lupus. Joint swelling, a symptom that can occur in lupus, is not a feature of fibromyalgia.
Chronic fatigue syndrome, also known as myalgic encephalomyelitis, primarily involves severe, debilitating fatigue that is not relieved by rest and worsens with physical or mental exertion. It can also cause muscle and joint pain, sleep problems, and cognitive issues. Unlike lupus, it is not an autoimmune disease and lacks the characteristic autoantibodies, systemic inflammation, or potential organ damage seen in lupus.
Distinguishing Lupus from Mimicking Conditions
Distinguishing lupus from similar conditions requires a comprehensive diagnostic approach. A diagnosis is not based on a single test; healthcare professionals, particularly rheumatologists, integrate a patient’s medical history, physical examination, and laboratory tests.
Diagnostic criteria, such as those from the American College of Rheumatology (ACR) or the European League Against Rheumatism/ACR (EULAR/ACR), provide a diagnostic framework. These criteria use a scoring system based on clinical signs and specific laboratory markers. A positive antinuclear antibody (ANA) test is often an initial screening step, present in most people with active lupus. However, a positive ANA alone does not confirm lupus, as it can be found in other autoimmune conditions or healthy individuals.
More specific blood tests confirm a lupus diagnosis and assess disease activity. These include highly specific anti-double-stranded DNA (anti-dsDNA) and anti-Smith (anti-Sm) antibodies. Other relevant tests include anti-Ro/SSA and anti-La/SSB antibodies, complement levels (C3, C4) (which can be low during active disease), and inflammatory markers like erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). A complete blood count and tests for kidney and liver function are also routine.
Urinalysis may check for kidney involvement. Biopsies of affected tissues, such as skin or kidneys, may be necessary to confirm diagnosis or assess organ damage. Accurate diagnosis is paramount for guiding appropriate management and treatment.