Skin changes in gout

Definition

1. Cutaneous changes during an acute gout attack

• Marked erythema, warmth, tenderness, and oedema of overlying skin.
• Skin may look tense and shiny due to oedema.
• As the acute inflammation resolves, the skin often becomes violaceous.
• Desquamation or peeling may follow as oedema subsides.
• Severe attacks may simulate cellulitis or septic arthritis.

2. Chronic tophaceous gout

Tophus

Time of appearance

• Generally develops after long-standing, insufficiently controlled hyperuricaemia and recurrent attacks.
• Commonly occurs around 10 years after onset of gout.
• Rarely, tophi may be the first manifestation, including in patients with a normal serum urate level.

Morphology

• Firm, painless dermal or subcutaneous papules and nodules
• Fusiform swellings
• Smooth or multilobulated masses
• Lesions ranging from pinhead size to very large deforming nodules
• Colour: skin-coloured, white-yellow, cream-coloured, or erythematous
• Skin may be thin and translucent, with prominent overlying vessels
• Deep tophi may not be readily visible clinically

Typical sites

• Helix and antihelix of ear, pinna
• Skin over small joints of fingers and toes, especially DIP and PIP joints
• Finger pads and palmar/ventral digital creases
• Olecranon bursa and extensor elbow
• Prepatellar region and knee
• Achilles tendon and other tendon sheaths
• Feet and first MTP joint

3. Ulceration and discharge

• Soften and break down
• Ulcerate
• Discharge clear fluid containing white flecks, or thick white, gritty, chalk-like material
• Heal and subsequently recur or break down again

4. Unusual cutaneous forms of gout

A. Intradermal or pustular tophi

• Fine intradermal deposits can clinically resemble pustules.
• They may appear as multiple white-yellow papules containing urate material.
• Can occur without prominent arthritis in rare cases.

B. Disseminated cutaneous gout

• Multiple widespread papules, nodules, or pustule-like lesions due to diffuse cutaneous urate deposition.
• May be seen in severe, chronic poorly controlled disease.

C. Gouty panniculitis

• Firm erythematous or skin-coloured subcutaneous nodules and plaques
• Usually on the lower limbs
• May be painful or tender
• Irregular surface and well-defined borders
• Can ulcerate and discharge chalky white material

D. Atypical locations

• Nasal bridge
• Eyelids and ocular structures
• Breast
• Larynx
• Heart valves

5. Histopathology

Typical findings

• Dermal or subcutaneous deposits of amorphous material.
• Needle-shaped clefts represent dissolved MSU crystals in routinely processed specimens.
• Foreign-body granulomatous response with:
  • Histiocytes
  • Multinucleated giant cells
  • Chronic inflammatory infiltrate
  • Fibrosis in older lesions

Polarized microscopy

• Fresh material shows long, slender needle-shaped MSU crystals.
• Crystals are negatively birefringent under compensated polarized light.

Important processing point

• Use absolute ethanol or an ethanol-based fixative such as Carnoy fluid.
• Fresh or frozen material may be examined under polarized light.
• In formalin-fixed tissue, unstained thick sections may still demonstrate crystals or crystal clefts.

6. Differential diagnosis of cutaneous tophi

7. Diagnostic approach in dermatology

• Consider gout in a patient with chronic hyperuricaemia, recurrent arthritis, renal impairment, diuretic use, or a history of gout who presents with yellow-white nodules or chalky ulceration.
• Serum urate supports the diagnosis but does not confirm it and can be normal.
• Best confirmation: aspiration or biopsy showing negatively birefringent needle-shaped MSU crystals.
• Exclude secondary infection in an ulcerated or discharging lesion by Gram stain and culture where indicated.

8. Treatment principles relevant to skin lesions

• Long-term urate-lowering therapy with sustained serum urate reduction is the key treatment.
• With adequate urate control, tophi may partly or completely regress.
• Manage ulcerated lesions with wound care and treatment of secondary infection if present.
• Surgical debulking/excision may be considered for large lesions causing ulceration, compression, severe deformity, functional impairment, or diagnostic uncertainty.

Exam takeaway