Dermatologic Manifestations of Nocardiosis Workup

Updated: Dec 27, 2019
  • Author: Brent A Shook, MD; Chief Editor: Dirk M Elston, MD  more...
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Laboratory Studies


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, [21] 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 blac Gomori methenamine silver stain demonstrating black filamentous Nocardia species.