Granulocytes are the predominant white blood cells released from the bone marrow. They are responsible for ingesting and killing or inactivating most infectious organisms, a process called phagocytosis. The granules referred to in the name are actually the lysosomes in the cell that contain caustic and digestive enzymes. These same enzymes are released outside the cells and help to break down and clean up the cellular debris of inflammation and injury. The most abundant granulocyte is the neutrophil.
About half of these cells circulate in the bloodstream while the rest reside in various places in the body where they can be released rapidly into the circulation when needed. Neutrophils are attracted to the site of inflammation by various chemical mediators.
The other much less numerous granulocyte is the eosinophil. These cells perform phagocytosis and also ingest yeasts and mycoplasma. The eosinophil is uniquely associated with parasitic infections and is particularly toxic to intestinal worms. Eosinophils are attracted to areas of infection and inflammation by factors released by lymphocytes, platelets, and mast cells, including histamine.
Neutrophils and eosinophils are rarely seen in biopsies of normal skin. However, in skin infections caused by Staph or Strep bacteria, neutrophils may become so abundant that they accumulate in pustules, boils, and abscesses that must be drained to relieve the pressure.
There are also some non-infectious diseases in which large numbers of neutrophils accumulate in the form of sterile pus. Examples of this are nodulocystic acne and a related condition called hidradenitis suppurativa in which deep abscesses develop with sinus tracts and disfiguring scars under the arms, breasts, pubic area, and groins. All of these areas of the body contain many apocrine sweat glands.
There is a skin disease called neutrophilic dermatosis or Sweet’s syndrome. The rash consists of red plaques that may be painful, with central clearing, and possibly blisters or pustules. The lesions resemble those of erythema multiforme. Fever, headaches, muscle and joint pain may accompany the rash along with an elevated white blood cell count. The cause is often not found, but Sweet’s syndrome may be associated with infection, malignancy, inflammatory bowel disease, and pregnancy. Diagnostic skin biopsy shows neutrophils distributed diffusely throughout the upper dermis.
The evaluation of Sweet’s syndrome includes ruling out all of the associated conditions mentioned above and stopping any unnecessary drugs. The primary treatment is high-dose corticosteroid such as prednisone or Medrol for several weeks. Relapses may occur in about one-third of cases after the dose of prednisone is gradually tapered. There are several second-line non-steroidal drugs that may be employed in the event of a relapse: dapsone, colchicine, potassium iodide, and minocycline.
Pyoderma gangrenosum is another example of an enigmatic condition which is not a primary infection despite the name which literally means “pus in skin with gangrene.” The rash begins as a small red bump, possibly around a hair follicle, and develops into a pustule which rapidly spreads outward with a purple border. The pustule breaks down in the center and ulcerates. The center becomes yellow with pus and dead tissue, and the borders of the ulceration become undermined. Severe pain may be associated with this process. Healing is slow and difficult and usually leaves disfiguring burn-like scarring.
Pyoderma gangrenosum may occur without any other underlying condition or in association with inflammatory bowel disease, leukemia, or rheumatoid arthritis. Features held in common with Sweet’s syndrome include neutrophils in the skin without infection and first-line treatment with prednisone. Second-line or combination treatments include the potent immunosuppressives Cyclosporine capsules and Remicade infusions. Safer but somewhat weaker and less expensive alternatives include dapsone, colchicine, minocycline, and sublesional injections of Kenalog. Successful treatment of any underlying disease often but not always aids in the healing of pyoderma gangrenosum.
One major difference between pyoderma gangrenosum and Sweet’s syndrome is that the former often demonstrates “pathergy,” that is, injury to the skin, including surgery, causes or exacerbates a lesion. Therefore, beyond diagnostic biopsy and cultures, no further surgery or debridements should be performed when pyoderma gangrenosum is suspected. Scar revisions should be delayed until the disease is inactive, and preventive doses of prednisone or cyclosporine should be considered during the perioperative period.
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