A 56 year old male is being evaluated for the low back pain. No history of trauma to back is elicited. He also complains of weight loss, fatigue and recurrent sinus infection. Examination revealed focal tenderness at the T10 level. Blood workup was done which revealed Hb of 9 g/dl. RFT were deranged as well. Skull x ray was done as shown. Bone marrow biopsy and serum protein electrophoresis was planned. What is the characteristic abnormality that will be evident in the patient on peripheral blood film?

**Core Concept**
The patient's presentation of low back pain, weight loss, fatigue, recurrent sinus infections, focal tenderness at the T10 level, and deranged renal function tests (RFT) suggests a diagnosis of multiple myeloma, a plasma cell dyscrasia characterized by the proliferation of malignant plasma cells in the bone marrow.

**Why the Correct Answer is Right**
Multiple myeloma is often associated with the production of monoclonal immunoglobulins, also known as M proteins. These abnormal proteins can accumulate in the bone marrow and cause various symptoms, including bone pain, anemia, and renal impairment. The presence of M proteins in the serum can be detected by serum protein electrophoresis (SPEP). On the peripheral blood film, the characteristic abnormality that will be evident in the patient is the presence of plasma cells or rouleaux formation due to the high levels of M proteins.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while anemia (Hb 9 g/dl) is a common feature of multiple myeloma, it is not a characteristic abnormality evident on the peripheral blood film.

**Option B:** This option is incorrect because while bone pain is a common symptom of multiple myeloma, it is not a characteristic abnormality evident on the peripheral blood film.

**Option C:** This option is incorrect because while renal impairment is a common complication of multiple myeloma, it is not a characteristic abnormality evident on the peripheral blood film.

**Clinical Pearl / High-Yield Fact**
In multiple myeloma, the presence of M proteins in the serum can lead to renal impairment due to the precipitation of these proteins in the renal tubules, causing cast nephropathy. This is an important clinical correlation to remember.

**Correct Answer:** C.

✓ Correct Answer: C. Rouleaux formation