26th January 2024

Differential Diagnoses

SLE can be difficult to diagnose, particularly in the initial stages, and the symptoms can be vague and overlap with many other more common causes. The most common symptoms include arthralgia, myalgia, fatigue, weight loss and photosensitivity. A definitive diagnosis in many cases may depend on antibody testing.

Rheumatoid Arthritis 

RA may also present with constitutional symptoms and arthralgia. However, characteristics such as morning joint stiffness and symmetrical, tender swollen joint would be more indicative of RA. In addition, joint deformities such as Boutonniere and Swan neck would be found in RA and not SLE. 

Positive tests such as Rheumatoid factor may be positive in both SLE and RA; however, Anti-CCP positivity would be expected in RA, while Anti-ds DNA positivity would be expected in SLE. 

Systemic Sclerosis 

Systemic Sclerosis may also present with arthralgia, rashes, and Raynaud’s phenomenon. However, features such as decreased joint mobility and skin induration would be more common in systemic sclerosis. 

Antibody testing is key here, where the presence of Anti-centromere and Anti-Scl-70 antibodies would be indicative of a diagnosis of sclerosis rather than SLE. 

Sarcoidosis 

Sarcoidosis may also present with features such as fatigue, fever, night sweats or a rash. However, symptoms such as cough and dyspnoea would be more common in sarcoidosis. In addition, an elevated angiotensin-converting enzyme and chest radiograph features such as bilateral hilar lymphadenopathy would be indicative of sarcoidosis rather than SLE. 

Adult-Onset Still’s Disease 

 While similar constitutional features such as fever and arthralgia may be present, splenomegaly would be more characteristic of Still’s disease. In both cases, laboratory blood testing may show elevated ESR and anaemia; however, Anti-ds DNA would be expected to be positive in SLE and not Still’s disease. 

Chronic Fatigue Syndrome 

This is a diagnosis of exclusion. Patients may present with vague symptoms, and blood tests, including inflammatory markers, metabolic panel and antibody testing, will all be within the normal range.