Sputum Cytology: Curschmann's Spiral or Parasite Larva?

Acellular bodies are usually observed when sputum cytology is performed under a light microscope. Among them, Curschmann's spirals are principally identified in association with pulmonary diseases such as bronchial asthma and chronic bronchitis.[1] Histochemical studies have demonstrated that Curschmann's spirals are structures with a complex composition, mainly formed by a central axis enriched with neutral mucins and sulfated and nonsulfated acid mucins, in contrast to an outer mantle enriched with neutral and nonsulfated acid mucins only.[2]

In contrast, artefacts and contaminants in cytological smears are one of the microscopic analysis challenges faced by the observer. The presence of arthropods, parts from their bodies, and larvae can be observed in sputum smears.[3] Inhalation and/or freshwater contamination are the most probable causes of the presence of these foreign bodies in cytological smears.[45] In addition, Curschmann's spirals have been also described as potential pseudoparasites in sputum smears.[6]

Here, we describe a curious observation in a sputum smear [Figure 1] from a 57-year-old smoker who consulted his physician for persistent cough. The sputum sample was obtained during spontaneous expectoration. The smear was fixed in 96% ethanol and stained using the Papanicolaou method. Initially, it was thought that the structure corresponded to a Curschmann's spiral, but upon careful examination, we focused on one morphological feature. The observed refractile tubular structure had a bilaterally symmetrical segmented shape with a size of approximately 200 × 40 μm. On both sides and along its entire body, numerous filiform projections, similar to hairs, were observed. Based on this morphology, the observed structure might be considered indicative of a moth or a carpet beetle larva. Both at the beginning and at the end of the structure, looping elongated masses of amorphous material were observed. Based on these findings, the following question was raised: Curschmann's spiral or parasite larva?

Figure 1

Striking structure detected in a sputum smear (Papanicolaou stain, 400×). After histochemical staining, the same striking structure showed positivity for sulfated (in black) and nonsulfated (in blue) acid mucin, which is observed in the box inserted in the top left corner (iron-diamine stain, 1000×)

Curschmann's spiral was favored by its relative frequency in sputum smears, absence of birefringence under polarized light, and presence of looping elongated masses of amorphous material at both ends. Conversely, the presence of an arthropod larva was favored by the striking appearance of the organism, with a refractile body and filiform projection-like hairs. Consequently, we decided to destain and restain the slide using a histochemical technique for mucins (high-iron diamine/Alcian blue staining). The observed structure in the sputum smear displayed positivity for sulfated acid mucin (in black) and non-sulfated acid mucin (in blue), and thus it was considered a Curschmann's spiral [see the box inserted in the top left corner, Figure 1].

Thus, whereas the different acellular bodies that are formed in the respiratory tract are usually recognized in sputum smears, any structure that can be inhaled into the respiratory airways is also capable of appearing in sputum smears and of raising challenges for the observer identify if this is not recognized. In certain situations, histochemical stains constitute a helpful tool for establishing the identification and nature of these structures.

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