malakoplakia

Etiology

• occurs in immunocompromised patients
  • rarely in patients with HIV1 infection due to preserved monocytic antimicrobial function
• infection most commonly due to Escherichia coli
  • Staphylococcus aureus, Pseudomonas aeruginosa, & Rhodococcus equi less common

Epidemiology

• rare, < 500 cases
• age range broad, median age at presentation is 53 years

Pathology

• presentation as friable yellow soft plaques
• inadequate killing of bacteria by macrophages or monocytes with defective phagolysosomal activity
• partially digested bacteria accumulate in monocytes or macrophages & lead to the deposition of calcium & iron on residual bacterial glycolipid
• result is basophilic inclusion structure, Michaelis-Gutmann body, pathognomonic for malakoplakia
• sheets of ovoid histiocytes with fine eosinophilic cytoplasmic granules (von Hansemann cells) seen on microscopy

Clinical manifestations

• most frequently affects genitourinary system
• can present as renal failure or pyelonephritis-like syndrome
• may involve other others including bone, lung, skin
• cutaneous manifestations
  • erythematous papules, subcutaneous nodules, draining abscesses, cutaneous ulcers, nonhealing surgical wounds, or draining fistulas

Laboratory

• culture of draining sinuses
  • bacterial culture for aerobic & anaerobic bacteria
  • mycobacterial culture
  • fungal culture

Diagnostic procedures

• skin biopsy
• fine needle aspiration or tissue biopsy as indicated
• electron microscopy may show Michaelis-Gutmann bodies (lysosomes filled with partially digested bacteria)

Management

• treatment with antibiotics that concentrate in macrophages (quinolones, trimethoprim-sulfamethoxazole) is associated with a high cure rate
• discontinuation of immunosuppressive therapy
• excision & drainage of subcutaneous abscesses

More general terms

• granulomatous disease
• infection (infectious disease)