What are the differential diagnoses for an elderly female with a history of osteoarthritis (OA) presenting with non-pitting edema?

Differential Diagnoses for Right Hand Non-Pitting Edema in Elderly Female with Osteoarthritis

In an elderly female with known osteoarthritis presenting with unilateral non-pitting edema of the right hand, the primary differential diagnoses include inflammatory osteoarthritis (particularly erosive hand OA), gout superimposed on pre-existing OA, psoriatic arthritis, rheumatoid arthritis, and less commonly, chronic non-bacterial osteitis or haemochromatosis.

Primary Considerations Based on Clinical Context

Erosive Hand Osteoarthritis

• Most likely diagnosis given the patient's OA history and non-pitting edema, which suggests bony rather than soft tissue swelling 1
• Erosive OA typically has abrupt onset with marked pain, inflammatory symptoms including soft tissue swelling and erythema, and targets interphalangeal joints (DIPJs and PIPJs) 1
• May present with mildly elevated CRP levels and has worse functional outcomes than non-erosive OA 1
• The non-pitting nature of edema suggests bony enlargement (Heberden or Bouchard nodes) rather than inflammatory synovitis 1

Gout Superimposed on Pre-existing OA

• Gout commonly superimposes on pre-existing hand osteoarthritis, complicating the clinical picture 1, 2
• Primarily affects metacarpophalangeal joints (MCPJs) of index and middle fingers, and wrists 2
• Presents with acute inflammatory episodes rather than chronic bony prominence 3
• Consider if patient has elevated urate levels or acute flare pattern 1

Psoriatic Arthritis

• May target DIPJs or affect just one ray (single finger involvement) 1
• Look for psoriasis (current, history, or family history in first-degree relatives), nail dystrophy, or dactylitis 1
• Juxta-articular new bone formation on radiography is characteristic 1

Rheumatoid Arthritis

• Mainly targets MCPJs, PIPJs, and wrists with symmetrical polyarthritis 1
• However, DIP joints can be involved in RA, though less commonly 1
• Consider if strongly positive RF or anti-CCP antibodies present 1
• Characteristic erosions on imaging 1

Secondary Considerations

Haemochromatosis

• Mainly targets MCPJs and wrists, similar to gout 2
• Consider in patients with family history or other systemic features of iron overload 1

Chronic Non-Bacterial Osteitis (CNO)

• Older age at onset and history of strain favor osteoarthritis over CNO 1
• CNO would show bony swelling with bone marrow edema on MRI and typically affects sternoclavicular joints, spine, or mandible more commonly 1

Critical Diagnostic Features to Assess

Clinical Examination

• Determine if swelling is truly bony (hard, non-mobile) versus soft tissue (inflammatory synovitis) 1
• Assess joint distribution: DIPJs/PIPJs suggest OA or erosive OA; MCPJs/wrists suggest RA, gout, or haemochromatosis 1, 2
• Examine for Heberden nodes (DIPJs) or Bouchard nodes (PIPJs), which are pathognomonic for OA 1
• Check for lateral deviation of interphalangeal joints or subluxation 1
• Assess for inflammatory signs: erythema, warmth, morning stiffness duration (>30 minutes suggests inflammatory arthritis) 1

Imaging

• Plain radiographs of both hands (posteroanterior view) are the gold standard 1
• Look for joint space narrowing, osteophytes, subchondral sclerosis, and subchondral cysts (classic OA features) 1
• Subchondral erosion indicates erosive hand OA 1
• Non-proliferative marginal erosions suggest RA 1

Laboratory Testing

• CRP/ESR: mildly elevated in erosive OA; significantly elevated suggests RA or infectious process 1
• Serum urate if gout suspected 1
• RF and anti-CCP if RA suspected (though not required for OA diagnosis) 1

Common Pitfalls to Avoid

• Do not assume all hand swelling in OA patients is simply OA progression—erosive OA, gout, and inflammatory arthritis can coexist 1, 2
• Non-pitting edema strongly suggests bony rather than inflammatory pathology, but erosive OA can have inflammatory features 1
• Unilateral presentation is atypical for RA (which is usually symmetrical) but can occur in psoriatic arthritis or gout 1
• Laboratory tests alone have limited sensitivity and specificity—diagnosis requires composite assessment of clinical features, joint distribution, and imaging 1