The case we present here is the patient was a 64-year-old female who had been diagnosed to have multiple myeloma, stage III B, type IgG kappa 17 years ago in 1993. She had received multiple lines of chemotherapy during this period. There was no history of other comorbidities such as diabetes, hypertension or tuberculosis. She was being treated with oral lenalidomide (25 mg for 21 days) and dexamethasone (40 mg on days 1, 8 and 15) of 28 days cycle for the current progression of myeloma. The baseline serum M band prior to the start of this regimen was 3.4 g/dl.
She presented on day 17 of the 2nd cycle with the complaints of profuse watery diarrhea, 10-12 times/day for the previous 15 days. The diarrheal product was non-bloody, without any mucus and not foul smelling. This was associated with nausea, mild crampy abdominal pain and a sense of fecal urgency without any fever. Physical examination was unremarkable except for tachycardia and signs of mild dehydration. There was anemia (hemoglobin of 9.7 g/dl) and leucopenia (white blood cells count 2800/mm3) but the absolute neutrophil count (1700/mm3) and platelets were normal. The liver and renal function tests were within normal limits but serum potassium was low (2.2 meq/L). Serological tests for HIV and hepatitis B and C were negative. The routine blood culture was sterile and the polymerase chain reaction test in peripheral blood for cytomegalovirus deoxyribonucleic acid was negative.
Stool examination showed 2-3 polymorphonuclear leucocytes per high power field with mucus but no visible or occult blood. No pathogen was seen on the gram stain and grown in culture. She was started on injectable cefoperazone-sulbactam and netilmicin but the diarrhea continued. Colonoscopy was performed, which suggested colonic mucosal inflammation likely to be infective in origin [Figure 1]. At this point, a diagnosis of cryptosporidial infection was suspected and the stool was submitted for examination with the modified Kinyoun acid-fast stain. This revealed multiple oocysts of Cryptosporidium parvum [Figure 2]. The patient was then started on oral nitazoxanide 500 mg 12 hourly for 10 days. The diarrheal frequency decreased after 5 days and it resolved completely by the 10th day of this drug. The patient was able to resume treatment with lenalidomide and dexamethasone later without any complications.