eMedicine Specialties > Dermatology > Bacterial Infections
Nocardiosis: Differential Diagnoses & Workup
Updated: Oct 30, 2009
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Differential Diagnoses
| Cellulitis | Leishmaniasis |
| Cutaneous Tuberculosis | Mycetoma |
| Dermatologic Manifestations of Pulmonary
Disease | Mycobacterium Marinum Infection of the
Skin |
| Ecthyma | Sporotrichosis |
Other Problems to Be Considered
Superficial skin infection: Streptococcal and staphylococcal infections are more common than nocardial infections. Maintain a high index of suspicion to diagnose infections with nocardial etiology. Notify the laboratory in advance when nocardiosis is suspected so that cultures are grown for longer than 48 hours.
Lymphocutaneous syndrome: Sporothrix schenckii is the most common cause. A dimorphic fungus causes sporotrichosis infection, and appropriate therapy includes excision, itraconazole, potassium iodide, or amphotericin B. When sophisticated culture techniques are unavailable, nocardiosis and sporotrichosis may be differentiated based on treatment response (nocardial lymphocutaneous syndrome also can be treated effectively with potassium iodide). Sporotrichosis typically follows a more indolent course and has a less inflammatory response compared with nocardiosis, although it also can be purulent.
Other less common causes of lymphocutaneous disease: These may be caused by non-Sporothrix fungi, such as Blastomyces, Coccidioides, Histoplasma, and Cryptococcus; bacteria, such as Francisella tularensis (tularemia), Staphylococcus aureus, and Streptococcus pyogenes; and viruses, such as herpes simplex and cowpox virus.
Mycobacterium marinum and other atypical mycobacteria: Along with Nocardia, M marinum is the most frequent cause of non-Sporothrix lymphocutaneous syndrome in the United States. Recent exposure to fresh- or salt-water sources (eg, fish tanks) provides an important historic clue. Treatment includes minocycline, trimethoprim-sulfamethoxazole (TMP-SMZ), and rifampin and ethambutol.
Leishmania brasiliensis: Infection is rare in the United States, but it is a relatively common cause of lymphocutaneous syndrome in the Middle East, Africa, Asia, and Latin America.
Mycetoma: The clinical presentation of mycetoma is distinctive. Determine the causative organism because treatment varies according to the infectious agent.
Workup
Laboratory Studies
- Culture: Nocardia species grow in most routine bacterial cultures. Maintain cultures for more than 48 hours because of the slow-growing nature of Nocardia compared with most other bacteria. Submit multiple clinical specimens for culture because smears and cultures are simultaneously positive in only one third of infections. Fungal and acid-fast bacillus cultures may help identify infection by other organisms that can resemble nocardial infection.
- CBC count: Peripheral leukocytosis often is present in acute forms of cutaneous nocardiosis and in systemic disease. Mild anemia can be found with chronic mycetomas.
Imaging Studies
- Perform chest radiography if dissemination from a pulmonary lesion is possible.
- Imaging studies typically are not necessary when a history of traumatic inoculation can be elicited. Local radiographs (eg, foot), CT scans, or MRIs may help in patients with deep infection (eg, mycetoma).
Histologic Findings
- Skin biopsy: Biopsy often reveals a dense mixed inflammatory infiltrate with suppuration (neutrophils prominent), granulation tissue, fibrosis, and granuloma formation.
- Gram stain: Prepare Gram stains from smears of draining areas, touch preparations of tissue, or sections of tissue. Nocardial organisms are thin, delicate, weak-to-strongly gram-positive organisms, and often form filaments. They often are stained irregularly or as beaded branching organisms, usually surrounded by many neutrophils. In cases reported by Satterwhite and Wallace,9 3 (50%) of 6 revealed gram-positive organisms and 100% revealed many neutrophils.
- Modified Kinyoun acid-fast stain: Nocardia species are weakly acid fast compared with the more strongly acid-fast Mycobacteria, decolorizing with a weak acid (1-2% sulfuric acid instead of acid alcohol).
- Sulfur granules (grains) examination: The size, shape, and color of the grains can help determine the causative agent in mycetoma. Grains can vary from 0.2-5 mm. White-to-yellow grains are usually seen in association with Nocardia, Actinomyces, Streptomyces somaliensis, Pseudallescheria boydii, and Cephalosporium. Brown-to-black grains are seen only in association with true dematiaceous fungi, such as Madurella and Phialophora jeanselmei. Red grains are seen in association with Streptomyces pelletieri.
- Sulfur granules are commonly seen in mycetomas but are seldom found in other cutaneous forms of nocardiosis. These granules appear to be a unique feature of primary cutaneous nocardiosis and are rarely noted with involvement of the lungs, brain, or other viscera.
- Sulfur granules caused by bacteria tend to contain filaments only 1-2 µm thick, while those caused by fungi have filaments that are 3-5 µm thick. Occasionally, filaments are seen more easily radiating outside of the granule.
- Hematoxylin and eosin stain: Nocardia organisms are not demonstrated with routine hematoxylin and eosin stain and may be seen only after a careful search of sections stained with Gram, Gomori methenamine silver, or acid-fast bacillus stain.
Gomori methenamine silver stain demonstrating black filamentous Nocardia species.
More on Nocardiosis |
| Overview: Nocardiosis |
 Differential Diagnoses & Workup: Nocardiosis |
| Treatment & Medication: Nocardiosis |
| Follow-up: Nocardiosis |
| Multimedia: Nocardiosis |
| References |
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Further Reading
Keywords
nocardiosis, nocardial infection, systemic nocardial disease, mycetoma, maduromycosis, Madura foot, soil-borne infection, soil infection, gardening injury
