A Case of Scedosporium Prolificans Osteomyelitis in an Immunocompetent Child, Misdiagnosed as Tubercular Osteomyelitis

Sir,

This is in response to the paper ‘Scedosporium infection in a patient with anti-TNFα therapy’ published by Caroline T Nguyen and Siba Raychoudhuri in the Indian Journal of Dermatology 2011;56(1):82-3,[1] which reports a case of Scedosporium in an immunosuppressed patient, we intend to further add to the existing knowledge by discussing our case who was immonocompetent and had osteomyelitis due to Scedosporium.

Scedosporium is a significant opportunist with very high levels of antifungal-resistance. This hyaline mold often produces localized disease, such as septic arthritis or osteomyelitis after penetrating injuries, or can lead to pneumonia or meningitis after aspiration of polluted water.[2] This report describes a patient with osteomyelitis caused by Scedosporium prolificans who was earlier diagnosed with tubercular osteomyelitis, and highlights the importance of microbiological diagnosis of the infections caused by this fungus.

We report a case of a 10-year-old immunocompetent boy who presented to the hospital with swelling of the right knee for last 2 years. He gave a history of fall from bicycle 2 years back subsequent to which he developed swelling and fever. Patient underwent an arthrotomy in a private hospital and was prescribed antibiotics. One month later, the patient reported to Lok Nayak Hospital, where he was diagnosed as a case of upper tibial osteomyelitis. The patient was taken for surgical debridement. The histopathologic examination results showed granulomatous reaction. Although microscopic examination and cultures were negative for Mycobacterium tuberculosis, a presumptive diagnosis of tuberculosis was made based on the histopathologic findings, raised ESR and a positive mantoux test. He was started on isoniazid, ethambutol, pyrazinamide and rifampin, and was given a knee brace.

The swelling subsided at that time, but the patient presented after few months to the hospital with swelling of the same knee with discharging sinus and fever. X-ray of the right knee showed osteolytic lesions of proximal end of tibia. Chest X-ray of the patient was clear. Surgical debridement and curettage was done again and pus was sent for AFB staining and culture, Bactec and for fungal culture. Direct microscopy of the sample showed septate hyphae, and culture was done on two tubes of Sabouraud's dextrose agar supplemented with chloramphenicol; one culture tube was incubated at 37°C and the another at 22°C. Fungal growth was observed on both the culture tubes after 5 days of incubation. The cottony colonies obtained on Sabouraud's dextrose agar were initially white, but became gray later. There was grayish-black pigmentation on reverse of Sabouraud's dextrose agar. Lactophenol cotton-blue mount showed numerous single-celled, ovoid, pale-brown, conidia, borne singly and in small groups on elongate, simple, and branched conidiophores. Since isolate did not produce any sexual state on Corn Meal Agar, it was identified as S. prolificans. The diagnosis was further supported by negative AFB staining, routine culture, and Bactec results. The orthopedician were intimated and suggested to start voriconaole based on literature review. The drug was started and the patient showed a remarkable improvement within 6 months.

This hyaline mold is seen to cause infection in immunocompromised individuals. However, in recent years it has been shown to be pathogenic in immunocompetent patients, who might acquire this infection, following subcutaneous traumatic or surgical implantation.[2–4] Osteomyelitis, mycetoma and septic arthritis are common presentations of this fungus.[4,5] This organism can also invade the lungs, kidneys, thyroid, eye, and brain.[6] Recently it has been reported to cause lymphadenitis in an immunocompetent individual.[7] These infections are very difficult to diagnose because of the clinical and histopathological similarities to other filamentous fungi, such as Aspergillus species, Fusarium species, and Sporothrix schenckii.[7] Some of the cases, where direct demonstration of the fungus is missed, may be misdiagnosed as tuberculosis based on the granulomatus reaction in histopathology and high prevalence of the infection in our country. Aspergillus and Fusarium species are usually susceptible to various antifungals but Scedosporium seldom responds to the same. Only a few antifungal agents have been shown to be effective against Scedosporium infections, like Voriconazole.[2,4] Due to its known resistance to antifungal agents, it is important to diagnose this infection in the early stage of the disease.

This case highlights the need for a discerning eye to look at all causes of chronic infections presenting with granulomatus reaction with a high-index of suspicion for a fungal infection. Special pains taken for identifying a fungal etiology in such chronic infections will go a long way in early management and reduction of morbidity.