Differentials
Rheumatoid arthritis
SIGNS / SYMPTOMS
May be difficult to differentiate clinically.
Patients with SLE frequently present with an inflammatory arthritis with a similar pattern to rheumatoid arthritis, although it tends to be less symmetrical.
INVESTIGATIONS
Joint x-rays demonstrate symmetrical, erosive arthritis.
Antiphospholipid syndrome
SIGNS / SYMPTOMS
Characterised by the occurrence of venous or arterial thrombosis or recurrent fetal loss in the presence of antiphospholipid antibodies.
INVESTIGATIONS
Antiphospholipid antibodies: anticardiolipin antibodies IgG or IgM present in moderate or high levels on ≥2 occasions at least 6 weeks apart and lupus anticoagulant detected on ≥2 occasions at least 6 weeks apart. These antibodies may also be positive in SLE.
About 10% of patients with antiphospholipid syndrome are b2-glycoprotein positive.[80]
Venereal Disease Research Laboratory (VDRL) test: false-positive result.
Systemic sclerosis
SIGNS / SYMPTOMS
Raynaud's phenomenon is present in almost all patients with systemic sclerosis, being the initial symptom in about 70% of patients.
Patients with SLE often have Raynaud's phenomenon as well, but these tend not to ulcerate compared with patients with systemic sclerosis.
Patients with systemic sclerosis have characteristic sclerodactyly and calcinosis, not present in SLE.
INVESTIGATIONS
Auto-antibodies: positive anti-centromere antibodies (limited cutaneous systemic sclerosis) or anti-topoisomerase 1 (Scl-70) antibodies (diffuse cutaneous systemic sclerosis).
Mixed connective tissue disease
SIGNS / SYMPTOMS
Mixed connective tissue disease (MCTD) is characterised by a combination of manifestations similar to those in SLE, systemic sclerosis, and myositis. Difficult to differentiate clinically.
INVESTIGATIONS
Auto-antibodies: positive anti-RNP antibodies are specific to MCTD.
Patients with MCTD tend to lack other antibodies such as anti-Sm, anti-Ro, anti-La, and anti-dsDNA.
Adult Still's disease
SIGNS / SYMPTOMS
A variant of juvenile rheumatoid arthritis characterised by seronegative chronic polyarthritis in association with a systemic inflammatory illness, which manifests as symptoms similar to those of SLE.
The fever in adult Still's disease usually occurs once or twice daily with marked temperature elevation and normal temperature in between.
The rash is often only seen during febrile periods and is a salmon-coloured macular or maculopapular non-pruritic lesion.
INVESTIGATIONS
Elevated ferritin has been reported in most patients. Ferritin should therefore be checked in patients presenting with such symptoms and, if elevated, lead to a suspicion of adult Still's disease.
Joint symptoms are similar to rheumatoid arthritis and joint erosions and fusion on x-ray may occur, unlike in SLE.
Lyme disease
SIGNS / SYMPTOMS
May be difficult to distinguish clinically.
History of possible erythema migrans or exposure to ticks.
INVESTIGATIONS
Lyme-specific IgM and IgG are positive.
Although the presence of antinuclear antibody is common, the presence of dsDNA and Smith antibodies are not.
HIV
SIGNS / SYMPTOMS
May be difficult to distinguish clinically.
History of exposure to risk factors for HIV.
INVESTIGATIONS
Serum HIV enzyme-linked immunosorbent assay test is positive.
Although the presence of antinuclear antibody is common, the presence of dsDNA and Smith antibodies is not.
Cytomegalovirus
SIGNS / SYMPTOMS
May be difficult to distinguish clinically.
May be asymptomatic.
INVESTIGATIONS
Cytomegalovirus serology is positive for infection.
Although the presence of antinuclear antibody is common, the presence of dsDNA and Smith antibodies is not.
Infectious mononucleosis
SIGNS / SYMPTOMS
May be difficult to distinguish clinically.
INVESTIGATIONS
Positive agglutination test, for example, monospot.
Although the presence of antinuclear antibody is common, the presence of dsDNA and Smith antibodies is not.
Haematological malignancy
SIGNS / SYMPTOMS
SLE may be difficult to distinguish clinically from haematological malignancy.
INVESTIGATIONS
Bone marrow, other histology or imaging tests may distinguish the diagnosis.
Auto-antibodies will be negative.
Glomerulonephritis
SIGNS / SYMPTOMS
Difficult to differentiate clinically if no other symptoms or signs associated with SLE are present (e.g., Raynaud's phenomenon, rash).
INVESTIGATIONS
Antibodies for dsDNA may be positive if SLE is the cause.
Renal biopsy may aid in diagnosis.
Chronic fatigue syndrome
SIGNS / SYMPTOMS
No other signs that are typically associated with SLE (e.g., Raynaud's phenomenon, rash) will be present
INVESTIGATIONS
Auto-antibodies will be negative.
Generalised tonic-clonic seizures
SIGNS / SYMPTOMS
May be difficult to differentiate clinically as seizures can be a feature of SLE. However, no other signs that are typically associated with SLE (e.g., Raynaud's phenomenon, rash) will be present.
INVESTIGATIONS
EEG will demonstrate epileptiform activity.
Brain MRI may demonstrate a lesion.
Auto-antibodies will be negative in epilepsy.
Fibromyalgia
SIGNS / SYMPTOMS
Poorly localised symmetrical musculoskeletal pain with no diurnal variation.
Poorly responsive to analgesics/non-steroidal anti-inflammatory drugs.
May co-exist with SLE.
Positive typical tender points.
INVESTIGATIONS
Diagnosis is typically clinical.
Auto-antibodies will be negative.
Depression
SIGNS / SYMPTOMS
Typically no systemic manifestations (e.g., rash) unless co-exists with SLE.
INVESTIGATIONS
Diagnosis is typically clinical.
Auto-antibodies will be negative.
Septic arthritis
SIGNS / SYMPTOMS
May be difficult to differentiate clinically if patient presents with monoarthritis and no other features of SLE.
INVESTIGATIONS
Joint aspiration or synovial biopsy yields positive culture.
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