Differential Diagnosis - 60F with GI Symptoms + New Fever, HR 118, BP 200/75, Rigors After Treatment

Tier 1 - Most Likely (High Priority)

1. Sepsis / Septic Shock (Early/Compensated)

• Diarrhea + abdominal pain are classic entry points for gram-negative bacteremia (E. coli, Klebsiella, Salmonella)
• Fever + rigors (shivering) + tachycardia (HR 118) = classic SIRS/sepsis triad
• The high BP (200/75) can be seen in early sepsis where catecholamine surge precedes vasodilation - some patients hypertensive before progressing to hypotensive shock
• Tintinalli's Emergency Medicine: "Patients with distributive shock from sepsis may present with fever and a history suggesting a focal site of infection (e.g., cough, sputum production, abdominal discomfort, diarrhea)"
• Source of sepsis: gut (GI infection seeding bloodstream), urinary tract (co-incidental UTI in 60F is very common), cholangitis, diverticulitis

2. Clostridioides difficile Colitis / Toxic Megacolon

• She may have been on prior antibiotics before this presentation (triggering C. diff)
• Metronidazole is actually used to treat mild C. diff but the presentation with fever, rigors, and abdominal pain suggests possible fulminant C. diff or complication
• Severe C. diff can cause bacteremia and sepsis with high fever and tachycardia

3. Pheochromocytoma Crisis ("The Great Mimic")

• Episodic hypertension (BP 200/75), tachycardia, fever, diaphoresis/rigors
• GI symptoms (nausea, diarrhea, abdominal pain) are classic presentations
• Often misdiagnosed as a GI illness initially
• Can be triggered by stress, dehydration, IV fluids, or certain medications
• Textbook of Family Medicine 9e: "Pheochromocytoma is often referred to as the 'great mimic.' Hypertension, tachycardia, pallor, palpitations..." are hallmarks
• This diagnosis is high priority given the extreme BP elevation (200/75) with fever + tachycardia

Tier 2 - Drug-Related (Must Exclude Urgently)

4. Drug-Induced Fever / Hypersensitivity Reaction to Metronidazole

• Metronidazole (Flagyl) can cause drug fever - fever + rigors appearing after administration
• Drug hypersensitivity syndrome can present with fever, tachycardia, and systemic inflammation
• Rare but well-documented; onset typically within hours of drug administration
• Fitzpatrick's Dermatology: "Fever and internal organ inflammation signifies a more serious reaction, known as the hypersensitivity syndrome reaction (HSR)"

5. Neuroleptic Malignant Syndrome (NMS) - If "Provas" = Prochlorperazine

• Prochlorperazine (Stemetil/Provas) is a dopamine D2 antagonist antiemetic
• NMS = fever + rigors + autonomic instability (hypertension + tachycardia) + altered mental status
• Onset can be within hours of a single dose in susceptible patients
• The triad of hyperthermia + autonomic instability (BP 200/75 + HR 118) + drug exposure strongly suggests this
• This is a life-threatening diagnosis that must be excluded

6. Serotonin Syndrome

• Less likely unless she was on SSRIs/SNRIs/triptans/tramadol at home
• Could interact with metronidazole (mild serotonergic properties reported)
• Presents with hyperthermia, tachycardia, diaphoresis, agitation, clonus

Tier 3 - Underlying Conditions Unmasked

7. Acute Cholangitis (Charcot's Triad / Reynolds' Pentad)

• Right upper quadrant pain + fever + jaundice (Charcot's) - may present as "abdominal pain"
• In a 60F with GI symptoms, biliary pathology is common
• Can cause rapid bacteremia with fever spikes and rigors
• BP elevation possible due to pain and catecholamine response

8. Acute Pyelonephritis / Urosepsis

• Very common in 60F, may co-exist with GI symptoms or be the primary cause
• Rigors, high fever, tachycardia are hallmarks
• Can cause hypertension through pain/catecholamine response
• May not have classic flank pain if GI symptoms dominate

9. Hypertensive Emergency with Autonomic Dysregulation

• Pre-existing hypertension poorly controlled, decompensated by pain, dehydration, and stress
• NS infusion could have precipitated fluid overload in a hypertensive patient
• However, does not explain the rigors and fever - these need a separate explanation

10. Thyroid Storm (Thyrotoxic Crisis)

• Can present with diarrhea, nausea, fever, tachycardia, and extreme hypertension
• Triggered by physiological stress (infection, dehydration)
• In a 60F with GI symptoms, could mimic an acute abdomen
• Fever + HR 118 + BP 200/75 fits the Burch-Wartofsky criteria for thyroid storm

Summary Table

Immediate Workup to Order

1. Blood cultures x2 (before any antibiotic change)
2. CBC, CMP, LFTs, lipase, lactate
3. Urinalysis + urine culture
4. Blood glucose, TSH/Free T4 (thyroid storm)
5. Serum/24h urine metanephrines (pheochromocytoma)
6. C. diff toxin PCR (stool)
7. CK, CPK (NMS - look for rhabdomyolysis)
8. Abdominal ultrasound (cholangitis, cholecystitis)
9. ECG (tachycardia etiology, arrhythmia)
10. Stop Prochlorperazine immediately if NMS is suspected

Clinical Pearl: The combination of BP 200/75 + HR 118 + fever + rigors after prochlorperazine administration in a 60F should make NMS and pheochromocytoma top-of-mind diagnoses, both of which are life-threatening and require urgent targeted workup. Do not anchor on "she has a GI infection" - the vitals are far too deranged for simple gastroenteritis.