Table 1: Differential diagnosis of arthritis in SLE patient.

Diagnosis	SITES	CLINICAL	RISK FACTORS	INVESTIGATION
Inflammatory arthritis	Hand joints, knee, frequently symmetrical.	Frequently presenting problem. May be associated with flare in other organs		No clear association with ESR, C3, and SLEDAI score
Septic arthritis	Hip, knee (frequently multiple sites)	Acute onset, hot effusion	Corticosteroid therapy, inflammatory arthritis, osteonecrosis	High CRP, Joint aspiration: type 3 inflammatory fluid (turbid or frank pus, white cell count > 50 000, > 70% of which are neutrophils), positive culture
Osteo-articular Mycobacterium Tuberculosis infection	Spine, Hip, Knee, Wrist	Insidious onset, possible constitutional symptoms	Corticosteroid therapy, other immunosuppressive therapies, lymphopenia, nephritis, inflammatory arthritis	High inflammatory markers. Synovial fluid Gene x-pert and TB culture, synovial biopsy
Osteonecrosis	Hip, knee (frequently multiple sites)	Cold effusion	High dose corticosteroid therapy, vasculitis, coagulopathy, antiphospholipid antibodies, Raynaud’s phenomenon	X- ray may be abnormal if advanced, frequently normal in early stages. MRI is investigation of choice.

ESR: Erythrocyte Sedimentation Rate, SLEDAI score: SLE Disease Activity Score, CRP: C - Reactive Protein, TB: Tuberculosis, MRI: Magnetic Resonance Image