Unmasking The Tiger Man: When Eosinophilic Myositis Mimics Sarcoidosis

Idiopathic inflammatory myopathies are a heterogeneous group of disorders with overlapping clinical and imaging features. Advanced imaging such as ¹⁸F-fluorodeoxyglucose positron emission tomography-computed tomography (¹⁸F-FDG PET-CT) is increasingly used. The "tiger man" sign is a rare nuclear imaging sign associated with sarcoid myopathy and has been previously described in only two case reports of non-sarcoid myopathy. Eosinophilic fasciitis and myositis lie within a spectrum of eosinophil-associated disorders, for which evidence-based treatment remains limited. In this context, histopathological insights may offer significant diagnostic and therapeutic value.

A 68-year-old male presented with pain and oedema of the lower legs and forearms, accompanied by recurrent nocturnal fever. He had a prior diagnosis of eosinophilic fasciitis two years earlier. Proximal muscle weakness of the upper legs was noted. Laboratory tests revealed systemic inflammation and elevated creatine kinase (CK) levels, suggestive of an inflammatory myopathy, while screening for infections and autoimmune serology was negative. 18F-fluorodeoxyglucose positron emission tomography-computed tomography (¹⁸F-FDG PET-CT) imaging demonstrated a "tiger man" sign, characterized by extensive patchy ¹⁸F-FDG uptake in the skeletal muscles of all four extremities. Histopathological analysis confirmed a T-cell-mediated, necrotizing eosinophilic myositis, with no evidence of sarcoidosis or malignancy. Treatment with tacrolimus and plasma exchange resulted in significant clinical improvement and regression of ¹⁸F-FDG PET abnormalities.

This is the third report of the "tiger man" sign in a patient with a non-sarcoid myopathy, thereby expanding the differential diagnosis for this imaging finding. Whole-body imaging can identify hypermetabolic yet clinically silent muscular regions, thereby guiding a more accessible and relevant site for biopsy. Histopathological findings can enhance diagnostic certainty and guide a more effective treatment.

A "tiger man" sign on ¹⁸F-fluorodeoxyglucose positron emission tomography-computed tomography imaging is a rare and characteristic sign in sarcoid myopathy, but it is not disease-specific.Whole-body imaging can identify hypermetabolic yet clinically silent muscular regions, thereby guiding a more accessible site for biopsy.Histopathological analysis can enhance diagnostic certainty and guide a more effective treatment in the context of difficult to treat or idiopathic myositis.