Small cell carcinoma of the bladder presenting with paraneoplastic syndrome of inappropriate antidiuretic hormone

Primary small cell carcinoma of the ureter with associated hyponatremia and rapid progression to bladder involvement: a case report

Background

Primary small cell carcinoma (SmCCa) of the ureter is rare. The majority of patients present with visible haematuria. Diagnosis is confirmed by histopathology. Associated hyponatraemia in GU lesion can be due SmCCa can be useful for early diagnosis aggressive ureteric tumors. The current management includes radical surgery or radiotherapy with concomitant chemotherapy to improve survival and quality of life.

Case presentation

We present a case of a 77 years female who was found to have unilateral hydronephrosis with a 5 cm filling defect in the distal ureter on CT urogram. Further staging showed organ-confined disease. Serum sodium levels were low at presentation. At the time of planned nephroureterectomy (NU), cystoscopy revealed a bladder tumor obstructing the right ureteric orifice. TURBT was performed instead. After TURBT, there was marked hyponatremia and histology was small cell carcinoma (SmCCa). Paraneoplastic SIADH was the likely cause. Neoadjuvant chemotherapy (NACT) followed by radiotherapy (RT) was chosen for definitive treatment. This resulted in an excellent response supported by radiological evidence of almost complete resolution of the tumor.

Conclusion

The presence of genitourinary lesion and hyponatremia should raise suspicion of paraneoplastic SIADH. The case suggests the emphasis of histological diagnosis of the genitourinary lesion with existing hyponatraemia to provide better outcome with NACT followed by definitive treatment. We share our experience of NACT and RT in the management of ureteric SmCCa extension to the bladder.