Fig. 6.8. A The very thin filaments of Nocardia brasiliensis (Brown-Brenn stain, x400), and B grain showing peripheral eosinophilic clubs (H & E, x200). C, D Nocardia asteroides in sputum. (A, B from Bittencourt and Londero 1995)

Fig. 6.9 A-D. The clinical appearance of nocardiosis. A Localized swelling around the ankle joint with multiple sinuses discharging pus: a patient from West Africa. B A similar grossly swollen foot and ankle with multiple sinuses, due to Nocardia asteroides: a patient from India. C A longstanding, but progressive nocardial infection in the foot of an African from Uganda. This foot was amputated. D The very painful chronic infection in the foot of a young woman from Uganda which also had to be amputated. (C, D courtesy of Dr. D. H. Connor)

Clinical Characteristics

Some pulmonary infections may have no clinical symptoms and may be self-limiting. In the progressive pattern of infection, the CNS and skin are less commonly infected than the lungs but few parts of the body are immune.

The most striking local clinical features are swelling and sinus formation, with draining pus (Fig. 6.9). When there is systemic infection, these patients present with fever, cough, sputum, chest pain, and symptoms of pneumonia, none of which is specific for nocardiosis. The lungs are the most common site of infection, and when the pleura and chest wall are involved, there will be multiple sinuses but minimal fibrosis. Central nervous system involvement may be asymptomatic or cause headache, a stiff neck, vomiting, convulsions, and, in some patients, mental symptoms or paralysis. This usually indicates a nocardial brain abscess. The eyes (particularly the retina) may be infected. Meningitis is not common and the cerebrospinal fluid does not have any characteristic changes. Spinal involvement, which often causes a paravertebral abscess seen on imaging, may be mistaken for tuberculosis. All the organs, including kidney, liver, spleen, peritoneum, adrenals, and heart, may be involved and there may be multifocal bone involvement. Organ and skeletal involvement can be difficult to recognize clinically, but imaging may provide much more information.

Localized mycetomas are described in detail in (Fig. 6.9) and under Madura Foot; Mycetoma; Maduromycosis (see section below).

Imaging Diagnosis

PULMONARY NOCARDIOSIS

If not superimposed on damaged lungs, the extent of the infection depends very much on the immune status of the patient. There is usually patchy consolidation in both lungs, with multiple small cavities which coalesce to form larger abscesses.

There may be solitary pulmonary masses, often well defined. These may cavitate: spread to the pleura and into the chest wall is common and results in pleural effusions, empyema, and pleural thickening (Fig. 6.10A-D). There is less fibrosis than in actinomycosis, but when the ribs are involved, there is an exuberant periosteal reaction and irregular motheaten bone destruction. Sinuses develop and subcutaneous nodules may appear, draining the chest wall. Hilar and mediastinal lymphadenopathy and direct spread to the mediastinum occur, but are a little less common than in actinomycosis.

Until there is sinus formation or direct involvement of the chest wall, the differential diagnosis from a pulmonary pyogenic infection or tuberculosis is very difficult. Nocardiosis must be considered whenever there are solitary pulmonary masses, particularly peripheral, or when any lung lesion fails to respond to adequate therapy. Aspiration biopsy may be necessary to establish the diagnosis.

SKELETAL NOCARDIOSIS

When the spine is involved a paravertebral abscess may be mistaken for tuberculosis or brucellosis. Nocardiosis infects vertebral bodies, causing bone destruction, compression and loss of vertebral height (Fig. 6.11). There can be sclerosis within the body of the vertebra. The disc space is usually spared, but the pedicles and transverse processes can be infected and become sclerotic. It is difficult to distinguish nocardiosis from tuberculosis and brucellosis, but in the latter the disc space usually narrows early in the infection.

Further examples of skeletal nocardial infections are shown in (Figs. 6.10E-G) and (6.12-6.16).