Sporotrichosis: causes, symptoms, diagnosis, and treatment

Sporotrichosis is a chronic infectious disease caused by Sporothrix schenckii complex in the skin, subcutaneous tissue, mucous membranes, and local lymphatic system, and occasionally can spread throughout the body, causing systemic lesions. Skin lesions are granulomas, probably accompanied by papules, pustules, nodules, plaques, ulcers, and scabs, often in the exposed areas such as face and extremities.


Causes

The pathogens are Sporothrix schenckii complex, composed of Sporothrix schenckii, Sporothrix globosa, Sporothrix brasiliensis, Sporothrix mexicana, and Sporothrix luriei.

Sporothrix schenckii complex is widely distributed in nature and is saprophytes of soil, woods, and plants. Exposure to materials contaminated with the fungi after skin trauma is the main route of transmission. Farmers, workers, gardeners, and miners are susceptible. The disease can be sporadic, occupational, or endemic.

The disease is a zoonotic disease. Due to the increase in domestic pets, animal-to-human infections are also increasing. The disease is transmitted by mainly animals, predominantly cats, rarely mosquito bites and close contact between persons. Inhalation of conidia can cause pulmonary infections, and the eyes, bones, joints, and digestive system may be involved due to the invasion of the skin or mucous membranes. Disseminated or systemic lesions may occur in immunocompromised patients.


Signs and Symptoms

The disease mainly occurs on the skin, mostly the exposed areas, and is occasionally present in the internal organs. Sporotrichosis can be divided into cutaneous sporotrichosis and extracutaneous sporotrichosis. The former includes fixed cutaneous sporotrichosis, cutaneous lymphatic sporotrichosis, and cutaneous disseminated sporotrichosis. The latter is mainly caused by hematogenous dissemination or respiratory infections.

Fixed cutaneous sporotrichosis

The disease occurs 1 - 4 weeks after infection. Skin lesions occur mostly on the exposed areas such as the face, neck, extremities, and dorsal hands, and there is a history of trauma in most patients. The lesions are manifested by solitary, red or dark red, inflammatory papule or nodule, probably accompanied by ulcers, abscesses, and scabs, which is termed primary sore of sporotrichosis. In addition, scaly patches, verrucous plaques, acneiform lesions, granulomas, and cysts can also be seen. Generally, regional lymph nodes are not invaded, and there are no subjective symptoms.

Figure 1 fixed cutaneous sporotrichosis

Cutaneous lymphatic sporotrichosis

The disease occurs mainly on the hands, forearms, face, and calves, often unilateral, with a history of trauma in most patients. The primary sore gradually expands and develops centripetally along the lymphatic vessels, and beaded inflammatory nodules extend gradually in size and number. Lymphangitis may occur between nodules, but swelling and pain of nearby lymph nodes are not obvious. Necrosis can occur in the center of the nodules, forming ulcers. Facial satellite lesions near the primary sore often occur.

Figure 2 cutaneous lymphatic sporotrichosis

Cutaneous disseminated sporotrichosis

This disease is less common and mostly secondary to cutaneous lymphatic sporotrichosis. Multiple, scattered skin lesions result from autoinoculation or hematogenous dissemination. The skin lesions are manifested by extensively scattered or locally dense, inflammatory nodules, plaques, cysts, abscesses, and ulcers. Fever and fatigue may be present. The disease mainly occurs in immunocompromised or immunodeficiency patients, such as alcoholics, patients with diabetes, sarcoidosis, tuberculosis, malignant tumors, organ transplantation, or long-term application of immunosuppressants, and AIDS patients. Early diagnosis and prompt treatment can result in good prognosis, and delayed diagnosis may lead to poor prognosis.

Figure 3 cutaneous disseminated sporotrichosis

Extracutaneous sporotrichosis

Osseous, periosteal, and synovial sporotrichosis mostly results from subcutaneous tissue lesions affecting the periostea and synovium, often involving bone masses, and can occur in the metacarpal bone, metatarsophalangeal bone, ulna, and femur. Sporotrichosis can cause joint swelling and restricted movement, with joint cavity effusion and positive stab culture.

Ocular sporotrichosis is mostly primary infection, and can affect the eyelid, lacrimal sac, and conjunctiva. The lesions are ulcers or gummas.

Systemic sporotrichosis is less common and is caused by hematogenous dissemination, and the invasion of the skin, bones, or muscles causes nephritis, orchitis, epididymitis, and mastitis, occasionally the liver, spleen, pancreas, thyroid, and myocardium may be involved, mostly in patients with diabetes, sarcoidosis, or long-term corticosteroid therapy.

Meningeal sporotrichosis is rare. Headaches, vertigo, and mental symptoms may occur. Sporothrix schenckii complex can be found in cerebrospinal fluid (CSF) cultures. CSF cell count and protein are increased.

Pulmonary sporotrichosis is also rare, mostly in alcoholics, may be manifested by miliary necrosis or cavity, as well as lesions in the hilar lymph nodes and bronchial lymph nodes.


Histopathology

The early tissue change is chronic granulomas, and lymphocytes, plasma cells, histiocytes, epithelioid cells, and few Langhans giant cells can be seen. The central granulomas are gradually purulent, resulting in abscesses, forming ulcers after rupture of the abscesses.

The typical tissue change is a dense infiltration in the subcutaneous tissue and dermis, which is roughly divided into three layers, that is, inner, middle, and outer layer. The inner layer is a chronic purulent area composed by many neutrophils and few lymphocytes and histiocytes. The middle layer is a tuberculoid infiltration area consisting of many epithelioid cells and few Langhans giant cells. The outer layer is a syphiloid infiltration area composed of plasma cells, lymphocytes, and fibroblasts. There are often no obvious boundaries between the inner, middle, and outer layers. The spores of Gram-positive sporothrix are present in tissues, especially in histiocytes, but are generally difficult to identify.

Visceral tissue changes are mainly miliary necrosis. There are neutrophils, lymphocytes, macrophages, and few giant cells near the necrotic area, as well as scattered or aggregated, round or oval spores, which can be found in PAS diastase stain.


Diagnosis

On the basis of clinical findings, sporotrichin skin test, and fungal microscopy, the disease can be diagnosed. PAS diastase stain, PCR, nested PCR, and peptide mass fingerprinting can assist in the diagnosis.


Treatment

The preferred treatment regimen is itraconazole 200mg orally once daily until 2 - 4 weeks after the skin lesions completely subside. Severe infection requires amphotericin B lipid preparations 3 - 5 mg/kg intravenously once daily followed by itraconazole orally for 12 months after good clinical responses. Meningitis and disseminated infections in HIV-infected patients require lifelong maintenance treatment with itraconazole. Posaconazole may be effective as well.