Hamstring Muscle Cramp Visualized on Bone Single-Photon Emission Computed Tomography/Computed Tomography Hybrid Imaging

It is well recognized that bone-seeking radiotracers localize in muscles sustaining an injury from various causes (e.g., strenuous physical activity, trauma, hereditary myopathies, inflammatory myositides, medications, electrical burns, etc.). This report presents the case of an active 50-yr-old man (body mass index = 29) that was recently referred to our nuclear medicine department for bone scintigraphy, for the skeletal staging of a newly diagnosed prostate adenocarcinoma. The scan findings were unremarkable for its oncological indication but revealed extraosseous radiotracer absorption in the medial region of the hamstrings bilaterally. Hybrid scintitomography (single-photon emission computed tomography) with computed tomography indicated that this uptake involved the semitendinosus muscle. On a more meticulous repeat history questioning, he recalled experiencing muscle cramps on both posterior thighs 5 days earlier, during intense work-related physical activity (plumbing) under warm environmental conditions. The combination of strenuous exercise with likely dehydration contributed to bilateral self-limiting heat cramps of the hamstrings, leading to an inconsequential localized minor rhabdomyolysis that was discovered coincidentally a few days later during a bone scan. Although extraskeletal absorption of bone-seeking radiotracers in muscles is widely documented as a result of exertion or injury, this is the first report of radiotracer absorption induced by cramping.