The cytopathology of Actinomyces, Nocardia, and their mimickers

Abstract

Nocardia species and Actinomyces species are 2 of the most commonly diagnosed filamentous bacteria in routine cytopathology practice. These genera share many overlapping cytomorphologic features, including their thin, beaded, branching, Gram-positive, GMS-positive filamentous structures that fragment at their peripheries into bacillary- and coccoid-appearing forms. Features that help distinguish between these 2 microorganisms include the width of their filamentous structures, the angles at which they branch, and their ability or lack thereof to retain a modified acid-fast stain. In addition to cytomorphologic overlap, overlap in clinical presentation is frequent with pulmonary and mucocutaneous presentations seen in both. Differentiating between Nocardia and Actinomyces is essential because patients with these infections require different approaches to medical management. Both antibiotic susceptibilities and the need for early surgical intervention as part of the treatment plan vary greatly among these 2 groups. This review focuses on the clinical presentation, cytomorphology and staining characteristics that can be useful in identifying and distinguishing between Nocardia and Actinomyces infections, as well as their mimickers.

Cutaneous nocardiosis with discharging sinus clinically mimicking tuberculosis diagnosed by cytology

“…As Nocardia is a partial acid‐fast bacteria, special stains such as modified ZN stain with 1% sulfuric acid instead of the traditional 20% sulfuric acid as decolorizer highlight the pink filamentous long branching bacilli . These are differentiated from most common Mycobacterium tuberculosis bacilli, which are short slender beaded bacilli.…”

“…There are certain clinical and morphological differences between these two despite belonging to the same Actinomycetales family. Nocardia “grains” are typically small in size of <1 mm, whereas Actinomyces have macroscopically visible “sulfur granules,” usually surrounded by the Splendore–Hoeppli phenomenon and granulomatous inflammation in microscopy . In addition to that, subtle features of Actinomyces like broader filaments and acute angulation may help in differentiating it from Nocardia species .…”

Role of FNA and Special Stains in Rapid Cytopathological Diagnosis of Pulmonary Nocardiosis

“…Differentiating Nocardia from its mimics with the help of special stains is essential because of antibiotic susceptibilities, and the need for early surgical intervention as part of the treatment plan is different [14]. Gram stain and culture studies were not performed on any of our cases due to limited aspiration material.…”

“…Morphologically, Nocardia needs to be distinguished from Actinomyces spp., which is another filamentous bacterium with similar morphological features including their beading, branching, and gram- and GMS-positive properties [14]. …”

Splendore‐Hoeppli phenomenon in a fine needle aspirate of cervicofacial actinomycosis

“…The SHP has been described in cell block sections and rarely also in smears from bronchial and bile duct brushings or washings, fine needle aspirates from subcutaneous breast, lung and liver masses, in patients suffering from botryomycosis, actinomycosis, actinomycetoma and eumycetoma, sporotrichosis and blastomycosis…”