Herpes zoster mimicking sciatica: A diagnostic pitfall in immunocompetent middle-aged adult with low back pain.

Herpes zoster (HZ) involving lumbosacral dermatomes can mimic sciatica, leading to diagnostic delays. While HZ is more common in older or immunocompromised individuals, it can occur in immunocompetent middle-aged adults, presenting diagnostic challenges due to atypical presentations, particularly in patients with chronic pain. We report a 40-year-old immunocompetent male with chronic low back pain who presented with an erythematous gluteal rash and acute radiating left leg pain following a chiropractic session. The rash was initially misdiagnosed as eczema at a dermatology clinic, and the leg pain was attributed to lumbar radiculopathy due to the temporal association with mechanical intervention. The patient's own attribution of symptoms, together with the initial clinical framing, led to a delay in recognizing the underlying viral etiology. By Day 6, the clinical evolution of the rash into grouped vesicles and the presence of marked allodynia, despite a negative straight leg raise test, supported the diagnosis of lumbosacral HZ. Treatment with oral famciclovir resulted in rapid symptomatic improvement. This case underscores the importance of considering HZ in the differential diagnosis of acute radicular pain, even in the absence of typical early vesicular eruptions. It also highlights how cognitive biases-such as anchoring to a musculoskeletal cause and framing by the primary dermatological complaint-can impede diagnostic reasoning. Clinicians should maintain a high index of suspicion for HZ in patients with unilateral radicular pain and remain vigilant against cognitive pitfalls to ensure timely antiviral intervention.