Excerpt from Malakoplakia

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Background

Malakoplakia is an inflammatory condition presenting as a plaque or a nodule that usually affects the genitourinary tract but may rarely involve the skin. Malakoplakia was first described in the early 1900s as yellow soft plaques that were seen on the mucosa of the urinary bladder. Microscopically, malakoplakia is characterized by the presence of foamy histiocytes with distinctive basophilic inclusions, which are known as Michaelis-Gutmann bodies.

Cutaneous malakoplakia is rare but presents in patients who are immunocompromised and have defects in macrophage function. Lesions are yellow-to-pink papules, but they can present as nodules or ulcerations and are often diagnosed only after biopsy. Cultures of the lesions can yield bacteria, most commonly Escherichia coli.

Pathophysiology

Malakoplakia is believed to result from the inadequate killing of bacteria by macrophages or monocytes that exhibit defective phagolysosomal activity. Partially digested bacteria accumulate in monocytes or macrophages and lead to the deposition of calcium and iron on residual bacterial glycolipid. The presence of the resulting basophilic inclusion structure, the Michaelis-Gutmann body, is considered pathognomonic for malakoplakia.

Studies have suggested that a decreased intracellular cyclic guanosine monophosphate (cGMP) level may interfere with adequate microtubular function and lysosomal activity, leading to an incomplete elimination of bacteria from macrophages and monocytes.

Frequency

United States

The total number of patients with malakoplakia is fewer than 500. Most patients have genitourinary tract disease, although involvement of the gastrointestinal tract and other visceral organs has been described. Cutaneous malakoplakia is rare, with fewer than 50 cases reported in the literature. Because this disease is often diagnosed after biopsy of nondescript lesions, the true incidence is most likely higher.

International

International frequency of malakoplakia is the same as in the United States.

Mortality/Morbidity

Malakoplakia most often occurs in patients who are immunocompromised. Often, malakoplakia is resistant to treatment, with a mean duration of the skin lesions of 3-6 months.

• Mortality in patients with malakoplakia is most often due to an underlying condition.
• Significant morbidity relates to the chronicity of the condition, which can resist local and systemic therapy. Draining sinuses, persistence of disfiguring skin lesions, and involvement of visceral organs constitute significant morbidity in patients with malakoplakia.

Race

Cutaneous malakoplakia is more commonly reported in whites (39%) than in African Americans (19%) or Asians (12%), although the patient's ethnic group is often not specified in case reports.

Sex

Cutaneous malakoplakia occurs with a male-to-female ratio of 2.3:1.

Age

Cutaneous malakoplakia presents in patients with a broad age range. The median age at the time of presentation is 53 years. Occurrence of the disease is associated more with the presence of an immunocompromised state affecting monocyte and macrophage function than with age.

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