Acute Intermittent Porphyria (AIP) is a rare metabolic disorder of heme biosynthesis, classically characterized by a triad of abdominal pain, neuropsychiatric symptoms, and autonomic instability. However, atypical presentations can lead to delayed recognition and potentially irreversible neurologic deficits. We present an unusual case of AIP manifesting as a progressive, symmetric polyneuropathy without abdominal or psychiatric symptoms.

A 57-year-old man with hypertension presented with rapidly progressive asymmetric weakness, initially affecting the right lower extremity and subsequently involving all limbs. He reported 8.2 kg unintentional weight loss and dysphonia but denied sensory loss, dysphagia, bowel/bladder dysfunction, or abdominal pain. Examination revealed proximal-predominant weakness with preserved reflexes and intact sensation. Laboratory evaluation showed mild hyponatremia; metabolic, autoimmune, and infectious studies were unremarkable. MRI of the brain and cervical spine was normal. Electrodiagnostic testing demonstrated a predominantly axonal sensorimotor polyneuropathy with chronic denervation changes. Cerebrospinal fluid showed mild protein elevation. Extensive evaluation for neuromuscular, metabolic, and toxic causes was unrevealing. Given persistent diagnostic uncertainty, urine porphyrin testing was performed, revealing markedly elevated uroporphyrin, coproporphyrin I/II, heptacarboxyl-, and pentacarboxyl-porphyrins, confirming AIP. Intravenous hemin therapy was initiated, leading to progressive improvement in muscle strength. Negative Inspiratory Force was monitored every four hours to detect respiratory decline.

The patient received intravenous immunoglobulin (IVIG) 30 g daily for 5 days prior to diagnosis without significant improvement. Once AIP was confirmed, intravenous hemin therapy was initiated. Following hemin infusion, the patient showed significant improvement in muscle strength across all extremities, documented through manual muscle testing over subsequent days.

This case showed the importance of clinical suspicion for Acute Intermittent Porphyria in patients presenting with rapidly progressive motor neuropathy, even in the absence of abdominal or psychiatric symptoms. Early recognition and prompt initiation of hemin therapy are critical to prevent irreversible neurological damage and respiratory failure.