A 28-year-old woman of Indian descent presents to the emergency department with acute severe abdominal pain, tachycardia, hypertension, and neuropsychiatric symptoms (confusion, anxiety). Urine dipstick is negative for blood and protein, but urine turns dark red on standing. Which of the following is NOT a characteristic feature of acute intermittent porphyria (AIP)?

Explanation

## Acute Intermittent Porphyria: Clinical and Biochemical Features ### Classification of Porphyrias ```mermaid graph TD A[Porphyrias]:::outcome --> B[Acute Porphyrias]:::outcome A --> C[Cutaneous Porphyrias]:::outcome B --> D[AIP - Neuropsychiatric]:::action B --> E[Variegate Porphyria - Mixed]:::action B --> F[Hereditary Coproporphyria - Mixed]:::action C --> G[Porphyria Cutanea Tarda - Photosensitive]:::action C --> H[Erythropoietic Protoporphyria - Photosensitive]:::action ``` ### Acute Intermittent Porphyria (AIP) **Key Point:** AIP is an **acute hepatic porphyria** characterized by neuropsychiatric and gastrointestinal manifestations, NOT photosensitivity or cutaneous lesions. | Feature | AIP | Variegate Porphyria | Porphyria Cutanea Tarda | |---------|-----|-------------------|------------------------| | **Enzyme defect** | PBGD ↓ | Protoporphyrinogen oxidase ↓ | Uroporphyrinogen decarboxylase ↓ | | **Acute attacks** | Yes (neuropsychiatric) | Yes (mixed) | No | | **Photosensitivity** | No | Yes | Yes | | **Skin lesions** | None | Blistering, scarring | Blistering, fragility | | **Urine findings** | ↑ δ-ALA, PBG (acute) | ↑ δ-ALA, PBG, copro | ↑ Uroporphyrin, heptacarboxyl | | **Stool findings** | Normal | ↑ Protoporphyrin | Normal | ### Clinical Presentation of AIP **High-Yield:** The classic triad of acute AIP: 1. **Abdominal pain** (colicky, severe, mimics surgical abdomen) 2. **Neuropsychiatric symptoms** (confusion, anxiety, psychosis, seizures, neuropathy) 3. **Autonomic instability** (tachycardia, hypertension, fever) **Clinical Pearl:** The dark urine in this patient is due to **porphobilin polymerization** (oxidation of porphobilinogen and δ-ALA), not hematuria — dipstick is negative for blood. ### Why Photosensitivity Is NOT a Feature of AIP **Warning:** Photosensitivity (blistering, scarring on sun-exposed skin) is characteristic of **cutaneous porphyrias** (variegate porphyria, porphyria cutanea tarda, erythropoietic protoporphyria) and **variegate porphyria** (which has both acute and cutaneous features). AIP is purely acute/neuropsychiatric. **Mnemonic:** **"AIP = Acute Intermittent Porphyria = Acute neuropsych, no skin"** ### Triggers of Acute AIP Attacks 1. Fasting and caloric restriction 2. Stress (physical, emotional, surgical) 3. Infections 4. Menstrual cycle (in women) 5. Drugs: barbiturates, sulfonamides, NSAIDs, oral contraceptives, phenytoin 6. Alcohol ### Management During Acute Attack - **IV glucose or hemin** (inhibits ALA synthase) - Avoid triggering drugs - Supportive care (analgesia, hydration) - β-blockers for autonomic symptoms [cite:Harrison's Principles of Internal Medicine 21e Ch 431]