What is the most likely diagnosis and recommended initial evaluation and treatment for a 43-year-old active-duty male with a 4‑day history of swelling and tenderness of the right fifth metatarsophalangeal joint, no warmth or fever, and dry, cracking skin?

Most Likely Diagnosis and Initial Management

The most likely diagnosis is acute gout affecting the right fifth metatarsophalangeal (MTP) joint, and you should immediately perform joint aspiration with synovial fluid analysis to confirm monosodium urate crystals and rule out septic arthritis. 1, 2

Differential Diagnosis

The clinical presentation strongly suggests acute gout based on several key features:

• Fifth MTP joint involvement is a common site for gout, though less classic than first MTP (podagra) 1, 2
• Rapid onset of pain and swelling over 4 days is consistent with crystal-induced inflammation, which typically reaches maximum intensity within 6-24 hours 1, 3, 2
• Active-duty military status suggests male gender, which increases gout likelihood 1, 2
• Absence of warmth and fever makes septic arthritis less likely but does not exclude it 4, 1
• Dry, cracking skin may reflect chronic skin changes or dehydration but does not rule out underlying crystal arthropathy 4

Alternative diagnoses to consider include:

• Psoriatic arthritis with dactylitis ("sausage digit"), though this typically presents with more diffuse toe swelling and is often associated with skin psoriasis 4
• Septic arthritis, which must be excluded given the joint swelling and tenderness 4, 1, 2
• Metatarsophalangeal joint synovitis from overuse or trauma 5

Essential Diagnostic Workup

Immediate Priority: Joint Aspiration

Joint aspiration with synovial fluid analysis is mandatory in this case because septic arthritis cannot be clinically excluded based on the absence of fever and warmth alone. 1, 2

The aspiration should include:

• Polarized light microscopy to identify needle-shaped, negatively birefringent monosodium urate crystals (sensitivity 63-78%, specificity 93-100%) 1, 2
• Gram stain and culture must be performed even if crystals are found, as gout and septic arthritis can coexist 4, 1, 2

Laboratory Tests

Order the following labs immediately:

• Serum uric acid level, though hyperuricemia alone does not diagnose gout and approximately 10% of acute gout patients have normal levels during an attack 1, 2
• Inflammatory markers (ESR, CRP) to assess inflammation severity 2
• Complete blood count to evaluate for infection 2
• Renal function (creatinine, eGFR) to guide medication choices 2

Imaging

If joint aspiration cannot be performed or is non-diagnostic:

• Ultrasound of the fifth MTP joint bilaterally is the first-line imaging modality, looking for the "double contour sign" (sensitivity 74%, specificity 88%) and evidence of synovitis with power Doppler signal 1, 2, 6
• Plain radiographs of the foot can exclude fracture and assess for chronic changes but have limited value for diagnosing acute gout 1, 2

Risk Factor Assessment

Evaluate for modifiable gout risk factors:

• Alcohol consumption (particularly beer) 1, 2
• Diet high in meat, shellfish, and high-fructose corn syrup 1, 2
• Medications: diuretics, low-dose aspirin, cyclosporine, tacrolimus 1, 2
• Comorbidities: obesity (RR 3.81), hypertension (RR 3.93), chronic kidney disease (RR 4.95), cardiovascular disease 1, 2

Initial Treatment Plan

If Gout is Confirmed (or Highly Suspected While Awaiting Results)

Initiate anti-inflammatory therapy immediately with one of the following options: 2

1. Low-dose colchicine: 1.2 mg loading dose, then 0.6 mg one hour later (total 1.8 mg), adjusted for renal function 1, 2
2. NSAIDs at full anti-inflammatory doses (if no contraindications such as renal impairment or cardiovascular disease) 2
3. Corticosteroids (oral, intra-articular, or intramuscular) if NSAIDs and colchicine are contraindicated 2

If Septic Arthritis Cannot Be Excluded

Do not start anti-inflammatory therapy until infection is ruled out. 4, 1

• Obtain joint aspiration with Gram stain and culture immediately 4, 1
• If clinical suspicion for infection is high, start empiric antibiotics after obtaining cultures 4

Common Pitfalls to Avoid

• Do not diagnose gout based on hyperuricemia alone—up to 80% of patients with hyperuricemia never develop gout, and 10% of acute gout patients have normal uric acid during attacks 1, 2
• Do not assume absence of fever and warmth excludes septic arthritis—joint aspiration is mandatory when infection cannot be clinically excluded 4, 1, 2
• Do not attribute the dry, cracking skin to the joint pathology without considering psoriatic arthritis, especially if there are other skin findings or nail changes 4
• Do not delay joint aspiration in favor of empiric treatment when the diagnosis is uncertain or this is a first attack 1, 2

Follow-Up Considerations

If gout is confirmed and this represents recurrent disease (≥2 flares per year), initiate urate-lowering therapy (allopurinol starting at 100 mg daily, titrated to target serum uric acid <6 mg/dL) after the acute flare resolves. 2