Acute Intermittent Porphyria and Acute Motor Axonal Neuropathy : Diagnostic Challenge in a Case of Severe Motor Neuropathy - A Case Report

Background : - Porphyrias are disorders of the biosynthetic pathway of heme. The neurological manifestations include acute and chronic peripheral neuropathy. Objective : - We present a case of acute intermittent porphyria-related neuropathology that, due to its neuropathological manifestation, was initially misdiagnosed as acute motor axonal neuropathy (AMAN), a form of Guillain-Barré Syndrome (GBS). Clinical Presentation: - A 28-year-old woman presented with progressive generalized weakness over a month, which acutely worsened. She reported difficulty combing her hair, rising from a seated position, gripping objects, walking, and having bilateral foot drops with a high-steppage gait. She also described intermittent abdominal pain for a few months, and mild symptom fluctuation with homoeopathic treatment. There was no history of sensory disturbance, fever, or genitourinary symptoms. Physical examination revealed bilateral wasting of the thenar and hypothenar muscles, bilateral wrist and foot drop, proximal upper limb strength of grade 4/5, distal upper limb strength of 1/5, and lower limb strength of 3/5. Reflexes were 1+ in the upper limbs and 2+ in the lower limbs, with intact sensation and unremarkable cerebellar and cranial nerve examinations. Initial workup favoured acute motor axonal neuropathy (AMAN), a Guillain-Barré syndrome variant, based on clinical presentation and albuminocytologic dissociation in CSF. However, the presence of dark urine and abdominal pain prompted further testing, which revealed an elevated urine porphobilinogen (PBG) level of 29 µmol/L (N<10 µmol/L), diagnosing acute intermittent porphyria (AIP). Meanwhile, nerve conduction studies revealed absent responses in the radial and peroneal nerves, accompanied by reduced compound muscle action potentials, slowed conduction velocities, and prolonged distal latencies in other nerves. Sensory studies showed only prolonged distal latencies in bilateral median nerves. EMG revealed acute denervation in multiple proximal and distal muscles. Based on clinical features, biochemical markers, and electrophysiological findings, a diagnostic conundrum arose between AIP-associated peripheral neuropathy and AMAN. Intervention and Outcomes: - Hemin, the specific treatment for AIP, was unavailable in this resource-limited setting. The patient was treated with high-concentration intravenous glucose and a trial of intravenous methylprednisolone (IVMP) despite limited supporting evidence. Mild improvement was observed, with upper limb proximal strength increasing from grade 3 to 4. At one-month follow-up, proximal upper and lower limb strength was grade 4, while distal upper limb strength remained at grade 1. Continued follow-up showed stabilization of neurological deficits, with no further improvement in muscle strength. Conclusion : - There is no direct link documented; Acute Intermittent Porphyria (AIP) may co-occur with or may mimic Acute Motor Axonal Neuropathy (AMAN). AIP can cause peripheral neuropathy due to small fiber and autonomic involvement, though its electrodiagnostic findings differ from AMAN. Physicians should consider AIP in suspected AMAN cases and perform appropriate clinical and laboratory investigation. Further research is needed to establish a definitive connection.