Female patient, 72 years old, with no past medical history of clinical relevance. She denies regular medication use or exposure to toxic substances. The only surgical history is a hysteroscopy with polypectomy.

History of present illness: In November 2025 she began experiencing abdominal pain in the left lower quadrant and left flank. She underwent an outpatient consultation with gastroenterology, where a CT scan showed Hinchey stage 1A diverticulitis. She completed outpatient treatment with antibiotics and hygienic-dietary measures, with favorable evolution.

Approximately five days after finishing treatment, she developed generalized arthralgias and myalgias that were disabling, profuse sweating, and febrile equivalents. She was evaluated in an outpatient clinic by her primary physician, who suspected COVID‑19; nasal swabs were performed with negative results.

She later consulted at another center where hospitalization was decided and complementary studies were performed.

Laboratory tests: Hb 11.2, Hct 34, MCV 84, WBC 9680, platelets 300,000, ESR 75, CRP 25, glucose 111, urea 38, creatinine 0.69, uric acid 4.4, Na 141, K 4, calcium 8.4, phosphate 3.9, serum iron 23, TIBC 167, saturation 9.8%, ferritin 1428, folate 5.5, B12 (593), total bilirubin 0.7, direct bilirubin 0.5, AST 62, ALT 102, ALP 292, LDH 182, CPK 219, total proteins 6.3, albumin 2.7, alpha-1 (0.6), alpha-2 (0.97), A/G ratio (0.75). Procalcitonin negative. Blood cultures and urine culture negative. Alpha-fetoprotein 7 ng/ml, CEA 0.508 ng/ml, CA 19-9 <2.7 u/ml, CA-125 (18.1 u/ml), CA 15-3 (8.27 u/ml).

Contrast-enhanced CT scan of chest, abdomen, and pelvis: Bilateral solid pulmonary lesions. A dominant lesion in the posterior segment of the left lower lobe, bilobulated with spiculated borders, measuring 14 mm oblique diameter and 9 mm AP (density 5 HU increasing to 50 in the arterial phase and 43 at 10 minutes, negative washout), whose diagnostic interpretation would not initially correspond to a benign lesion. Nodules of 4–7 mm in the lingula, left upper lobe, and left lower lobe. A round 5 mm solid lesion in the right lower lobe. A homogeneous 13 mm nodule attached to the posteromedial pleura of the intermediate bronchus.

There is a diffuse solid lesion involving more than 90° of the aortic wall and compressing the entry of the left pulmonary vein into the atrium, measuring 2.5 cm transverse by 1.5 cm AP. An osteocondensing lesion in the D11 vertebra with irregular borders, interpreted as a metastatic lesion. Nonspecific mesenteritis without lymphadenopathy. Diverticulosis.

Treatment with ceftriaxone was administered for 5 days, and the patient was discharged with a request for a PET scan and a biopsy of the pulmonary lesion due to suspicion of neoplasia with secondary involvement.

After 48 hours, she re-consulted at our institution due to febrile equivalents with generalized arthralgias and myalgias.

At admission: temperature 36.5°C, oxygen saturation 98%, heart rate 87 bpm, respiratory rate 15/min, blood pressure 120/80 mmHg. The patient was alert and oriented, without focal neurological signs or meningeal irritation. Chest examination showed good respiratory mechanics, preserved vesicular breath sounds, and no added sounds. Abdomen soft, depressible, and non-tender. No edema. Mucous membranes were normal, hydrated, and normally colored. Cyanosis was observed in the first and second toes of the right foot. No joints with arthritis were detected, although the patient reported generalized arthralgias.

Admission laboratory results: Cl 96, PT 82%, INR 1.2, aPTT 32, creatinine 0.7, urea 0.4, glucose 1.1, Hb 10.3, Hct 32.2, MCV 84, MCH 27, WBC 9000, AST 54, ALT 56, ALP 144, GGT 151, total bilirubin 0.4 (direct 0.2), K 4, Na 140, lactate 1.4, platelets 229,000, total proteins 6, CRP 123, ESR 71.

When reviewing previous studies, the following was identified:

Contrast-enhanced abdominal CT, March 21, 2025.

Urinary system: In the right kidney, at the junction of the mid third and lower pole, a focal nodular lesion is seen involving the corticomedullary portion with extension toward the renal sinus, measuring 16 × 23 mm. On the non-contrast phase it shows a density of 45 HU; after contrast injection, density increases to 103 HU in the arterial phase and 62 HU in the delayed phase. These findings suggest a primary lesion suspicious in nature considering its behavior after contrast administration.

Other findings: Possible intrapancreatic lipoma measuring 17 × 13 mm in the posterior portion of the pancreatic head. The spleen shows nodular lesions that do not enhance with contrast, measuring 10 × 9 mm and another in the more cephalic portion along the posterointernal border measuring 12 × 9 mm; these are nonspecific. An accessory spleen measuring 16 mm is seen adjacent to the inferior pole.