# Idiopathic Inflammatory Myopathy With Normal Creatine Kinase Levels in an Elderly Patient: A Diagnostic Challenge

## TL;DR

This paper presents a case of an elderly patient with a rare muscle disorder that was difficult to diagnose due to normal creatine kinase levels and misleading symptoms.

## Contribution

The study highlights the diagnostic challenges of idiopathic inflammatory myopathy in elderly patients with normal CK levels and emphasizes the need for comprehensive evaluation.

## Key findings

- An elderly male with chronic lower limb weakness was initially misdiagnosed due to misleading inflammatory markers and normal CK levels.
- Diagnosis of idiopathic inflammatory myopathy was confirmed through antibody testing, MRI, and muscle biopsy findings.
- The patient showed significant recovery after treatment with corticosteroids and mycophenolate mofetil.

## Abstract

Myositis is an inflammatory muscle disorder characterised by progressive weakness, and in elderly patients, diagnosis can be challenging due to symptom overlap with age-related conditions and misleading inflammatory markers. We describe an elderly male with chronic lower limb weakness initially attributed to infection based on elevated inflammatory markers, with persistently normal creatine kinase (CK) levels delaying recognition. Subsequent investigations revealed positive Mi-2 antibodies, an MRI demonstrating bilateral muscle oedema with increased signal intensity, and muscle biopsy findings of HLA class I upregulation with focal complement deposition, consistent with idiopathic inflammatory myopathy. The patient responded well to corticosteroids and mycophenolate mofetil, achieving significant functional recovery. This case underscores the diagnostic difficulties of idiopathic inflammatory myopathy in the elderly, particularly when CK is normal, where initial misattribution to infection led to diagnostic delay and significant functional decline, highlighting the importance of comprehensive evaluation to avoid misdiagnosis and enable timely treatment.