• Clinical science

Nocardiosis

Abstract

Nocardiosis is a rare infection caused by Nocardia, a genus of aerobic, gram-positive bacteria. It manifests as either pulmonary, cutaneous, or disseminated disease. Pulmonary nocardiosis presents as a virulent form of pneumonia, which occurs more commonly in immunosuppressed individuals. As in any other type of pneumonia, productive cough, pleuritic chest pain, and fever are the dominant symptoms, making it difficult to differentiate from other lung infections. Cutaneous nocardiosis manifests with either cellulitis or purulent erythematous nodules. It may be accompanied by inflamed lymph nodes. The disseminated form predominantly occurs in immunocompromised patients and is typically associated with pulmonary or CNS involvement. A suspected diagnosis is confirmed via culture from infected material (e.g., sputum or skin samples). The mainstay of treatment is long-term antibiotic therapy with TMP/SMX. Without treatment, pulmonary nocardiosis and disseminated nocardiosis are usually fatal in immunocompromised patients.

Epidemiology

  • > (3:1)
  • Purely pulmonary involvement: ∼ 40% of cases
  • Systemic infection: : ∼ 30% of cases (with the CNS being involved in about half of systemic cases)

References:[1]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

References:[1][2]

Clinical features

Pulmonary nocardiosis

The symptoms of fever, chills, and weight loss often result in pulmonary nocardiosis being mistaken for tuberculosis!

Cutaneous nocardiosis

  • Primary infection
    • Superficial cutaneous: cellulitis; (pain, swelling, erythema, and warmth), nodules, abscesses, ulceration
    • Lymphocutaneous: superficial cutaneous infection + regional lymphadenopathy and lymphangitis
    • Subcutaneous mycetoma: chronic pyogenic lesion of the extremities (usually affecting the feet, back and hands) → painless indurated nodule → draining sinus tract
  • Cutaneous involvement from a disseminated focus

Disseminated nocardiosis

  • Definition: two or more sites of involvement
  • Generally involves both the lungs and the brain
    • Pulmonary findings are prominent (up to 40% of cases).
    • Metastatic abscesses may be found almost anywhere, but are predominantly located on the lower extremities.
    • CNS features (∼ 45% of cases); : headache, lethargy, confusion, seizures, sudden onset of neurological deficits

The combination of pneumonia and abscess in the lower extremity is particularly suggestive of nocardiosis!

References:[3][4][5][6]

Diagnostics

  • Culture (confirmatory test ): from sputum, skin biopsy samples, CSF fluid, or pus from the cutaneous lesions
    • Gram-positive aerobic bacilli, weakly acid-fast; , branching filamentous rods
  • Imaging:
    • Chest x-ray or CT: pulmonary nodules; (with or without cavitation), pulmonary infiltrates (reticulonodular pattern or diffuse), abscess, empyema
    • Cranial CT or MRI: brain abscesses

References:[5][6]

Treatment

References:[6][7][8]