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Skin-Colored Nodule on the Scalp of a Middle-aged Man

Educational Objective
Based on this clinical scenario and the accompanying image, understand how to arrive at a correct diagnosis.
1 Credit CME

An otherwise healthy man in his 40s presented with a 3-month history of an asymptomatic nodule on his scalp. There were no systemic complaints, history of arthropod bite, immunosuppression, travel abroad, or contact with animals in the recent past. Physical examination revealed a skin-colored, firm, nontender, freely mobile 2 × 1.5-cm nodule with overlying normal skin on the right occipital region of the scalp (Figure, A). There was no lymphadenopathy. No other cutaneous lesions were present.

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B. Subcutaneous dirofilariasis

Subcutaneous dirofilariasis is a zoonotic infection caused by filarial nematode Dirofilaria, a natural parasite of dogs, cats, and wild animals. It is mostly reported in South America, Europe, Southeast Asia, and Africa.1,2 The dog parasite Dirofilaria repens is the most common agent for human infections acquired accidentally by the bite of mosquitoes of the genera Culex, Aedes, and Anopheles.1 Clinical forms include pulmonary, subcutaneous, and ocular disease.3 Subcutaneous dirofilariasis presents as an occasionally migratory nodule that may be painful or itchy, distributed on the face (especially periorbital and subconjunctival), chest wall, upper arm, thigh, and male genitalia.13 As the adult female worm does not reach maturity in skin, microfilariae usually are not seen in blood. However, microfilariae have been reported in subcutaneous tissue.4 Diagnosis is usually established on macroscopic analysis of the parasite morphology or microscopic examination of histologic sections from the nodule. Excision of the nodule is both diagnostic and therapeutic. Adult worms have a multilayered thick-walled cuticle with longitudinal ridges and transverse striations, which appear as regularly spaced, round, elevated structures about 10 to 12 μm apart, and a well-developed muscular layer. Adult worms are 50 to 170 mm long and 370 to 650 μm wide.1 Polymerase chain reaction has been used in skin, eye, and pulmonary specimens for species confirmation and where histomorphology is inconclusive.57 Peripheral eosinophilia is an inconsistent finding. Antibody detection using enzyme-linked immunosorbent assay is of little diagnostic value owing to low sensitivity and specificity.1 Slitlamp examination and chest radiograph should be performed to rule out ocular and pulmonary involvement, respectively.

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Article Information

Corresponding Author: Geeti Khullar, MD, DNB, Department of Dermatology and Sexually Transmitted Diseases, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi-110029, India (geetikhullar@yahoo.com).

Published Online: September 23, 2020. doi:10.1001/jamadermatol.2020.3527

Conflict of Interest Disclosures: None reported.

Additional Contributions: We thank the patient for granting permission to publish this information.

References
1.
Tzanetou  K , Gogou  C , Giannoulopoulos  A , Patralexis  C , Fragia  K .  Fibrous subcutaneous nodule caused by Dirofilaria repens.   Travel Med Infect Dis. 2009;7(5):318-322.PubMedGoogle ScholarCrossref
2.
Lupi  O , Downing  C , Lee  M ,  et al.  Mucocutaneous manifestations of helminth infections.   J Am Acad Dermatol. 2015;73(6):929-944.PubMedGoogle ScholarCrossref
3.
Sukumarakurup  S , Payyanadan  BM , Mariyath  R , Nagesh  M , Moorkoth  AP , Ellezhuthil  D .  Subcutaneous human dirofilariasis.   Indian J Dermatol Venereol Leprol. 2015;81(1):59-61.PubMedGoogle ScholarCrossref
4.
Damle  AS , Iravane Bajaj  JA , Khaparkhuntikar  MN , Maher  GT , Patil  RV .  Microfilaria in human subcutaneous dirofilariasis.   J Clin Diagn Res. 2014;8(3):113-114.PubMedGoogle Scholar
5.
Nazar  N , Lakshmanan  B , Jayavardhanan  KK .  Molecular characterization of human Dirofilaria isolates from Kerala.   Indian J Med Res. 2017;146(4):528-533.PubMedGoogle Scholar
6.
Montesel  A , Bendinelli  A , Figus  M , Posarelli  C .  There is a worm in my eye!   Eur J Ophthalmol. 2019;29(5):NP5-NP8.PubMedGoogle ScholarCrossref
7.
Ferrari  PA , Grisolia  A , Reale  S , Liotta  R , Mularoni  A , Bertani  A .  A rare case of human pulmonary dirofilariasis with nodules mimicking malignancy.   J Cardiothorac Surg. 2018;13(1):65.PubMedGoogle ScholarCrossref
8.
Okulicz  JF , Stibich  AS , Elston  DM , Schwartz  RA .  Cutaneous onchocercoma.   Int J Dermatol. 2004;43(3):170-172.PubMedGoogle ScholarCrossref
9.
Khullar  G , Agarwal  D , Chandra  M .  Solitary subcutaneous nodule in the preauricular region.   Int J Dermatol. 2020;59(2):173-174.PubMedGoogle ScholarCrossref
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