What is the likely diagnosis and recommended initial workup for base-of-thumb pain that is worst on waking, with swelling, bruising-appearing discoloration, and paresthesia, in a patient without known trauma?

Base of Thumb Pain Worse Upon Waking: Likely Diagnosis and Initial Workup

Start with plain radiographs of the thumb/hand as your initial imaging study, and consider acute calcific periarthritis, thumb carpometacarpal (CMC) osteoarthritis, or flexor pollicis longus tenosynovitis as your primary differential diagnoses given the acute onset with swelling, bruising-like discoloration, and paresthesia without trauma.

Clinical Reasoning and Differential Diagnosis

The constellation of symptoms—base-of-thumb pain worst on waking, swelling, bruising-appearing discoloration, and paresthesia without known injury—suggests several possibilities:

Most Likely: Acute Calcific Periarthritis (ACP)

• ACP of the thumb presents with acute severe pain, swelling, and can mimic inflammatory arthritis or infection 1
• The "bruising" appearance may represent inflammatory changes around calcium deposits
• Morning symptoms are characteristic of inflammatory conditions
• This is commonly misdiagnosed due to low prevalence and overlap with more common conditions 1

Alternative: Thumb CMC Osteoarthritis with Acute Flare

• Morning stiffness and pain are hallmark features 2
• Can present with swelling and inflammatory signs during acute exacerbations 3
• The paresthesia could indicate concurrent nerve involvement

Consider: Flexor Pollicis Longus Tenosynovitis

• Can cause paresthesia by compressing the radial digital nerve 4
• Presents with pain, swelling at thumb base
• Symptoms worsen with thumb movement 4

Initial Workup Algorithm

Step 1: Plain Radiographs (MANDATORY)

Obtain PA, lateral, and oblique views of the thumb/hand 5

• Look for calcium deposits (diagnostic for ACP) 1
• Assess for CMC joint space narrowing, osteophytes, subluxation (CMC OA) 6, 7
• Rule out occult fracture despite negative trauma history

Step 2: Physical Examination Focus

Specific findings to document:

• Palpation: Exact location of maximal tenderness—CMC joint vs. flexor tendon sheath 6, 7
• CMC grind test: Pain with axial compression and rotation of thumb metacarpal 6
• Range of motion: Document any triggering or clicking (suggests tenosynovitis) 8
• Sensory testing: Map the exact distribution of paresthesia—radial digital nerve territory suggests tendon sheath compression 4
• Inspection: True bruising vs. inflammatory erythema; degree of swelling 7

Step 3: If Radiographs Are Negative or Equivocal

Ultrasound is your next best study 5, 9

• Excellent for visualizing tendon pathology, tenosynovitis, and calcium deposits 5
• Can identify flexor pollicis longus tendinitis compressing digital nerve 4
• Real-time dynamic assessment of tendon movement
• Alternative: MRI without contrast if US unavailable or if concern for occult fracture persists 5, 10

Step 4: Laboratory Studies (Selective)

Only if inflammatory arthritis suspected:

• CRP/ESR (mildly elevated in erosive OA or inflammatory conditions) 3
• Consider rheumatoid factor, anti-CCP if multiple joint involvement
• Do NOT delay imaging for labs—radiographic findings are diagnostic

Critical Pitfalls to Avoid

1. Missing ACP: Radiographs are essential because calcium deposits are diagnostic but easily overlooked 1, 11. Don't assume "no trauma" means "no acute pathology"

2. Overlooking nerve compression: Paresthesia in thumb base pain suggests flexor tendon sheath pathology compressing the radial digital nerve—this requires ultrasound for diagnosis 4

3. Assuming chronic OA: While CMC OA is common, the acute presentation with "bruising" and paresthesia suggests a superimposed acute process 2

4. Inadequate radiographic views: A single view is insufficient—obtain at least 3 views including dedicated thumb projections 5, 6

Management Considerations Based on Diagnosis

If ACP Confirmed (Calcium Deposits on X-ray):

• NSAIDs for acute pain relief 12
• Consider aspiration of calcium deposits if severe
• Symptoms typically resolve with conservative management 1

If CMC OA with Acute Flare:

• Intra-articular corticosteroid injection may provide short-term relief (1 month), though evidence is limited 2
• NSAIDs for symptom control 12
• Thumb spica splinting for rest period
• Surgery reserved for severe, refractory cases after conservative treatment failure 2

If Flexor Tenosynovitis:

• Ultrasound-guided intervention if conservative measures fail 8
• Rest, NSAIDs, possible corticosteroid injection 12

The key is obtaining radiographs immediately—they will either show diagnostic calcium deposits (ACP), degenerative changes (OA), or be normal/equivocal (prompting ultrasound for soft tissue evaluation) 5, 1.