Diagnosis: Abdominal Wall Pain (Myofascial Abdominal Pain)
The most likely diagnosis is abdominal wall pain originating from the musculature or fascia of the abdominal wall, given the characteristic relief with muscle relaxants. This presentation strongly suggests a musculoskeletal rather than visceral etiology 1.
Diagnostic Approach
Key Clinical Features to Identify
- Carnett's sign: Pain that increases (or fails to decrease) when the abdominal muscles are tensed by having the patient lift their head and shoulders off the examination table while you palpate the painful area 1
- Localized tenderness: Pain confined to a circumscribed site in the abdominal wall, reproducible with digital palpation 1
- Anatomic distribution patterns 1:
- Semilunar line (most common - 71% of cases)
- Linea alba between xiphoid and umbilicus
- Within the rectus muscle itself
- Along the costal arch
Associated Risk Factors to Assess
- Obesity (BMI >30): Associated with chronic strain on abdominal wall structures 1
- Repetitive straining: History of chronic constipation with straining during defecation 1
- Exercise-related: Repeated forceful contractions of abdominal muscles 1
- Anxiety or depression: Present in many patients with chronic unexplained abdominal pain 1
Imaging Considerations
- Ultrasound as first-line: Can identify abdominal wall relaxation by demonstrating decreased muscle thickness (mean 38% reduction on affected side), continuity of fascia, and identification of all muscle layers 2
- MRI for confirmation: Reserved for cases where diagnosis remains uncertain after ultrasound 2
Treatment Protocol
First-Line Pharmacological Management
Cyclobenzaprine 5 mg three times daily is the recommended first-line muscle relaxant, with the strongest evidence base for musculoskeletal conditions 3, 4. This agent has been demonstrated superior to diazepam in multiple trials and has consistent efficacy data 4.
- Start with 5 mg TID rather than 10 mg to minimize adverse effects 4
- Treatment duration should be limited to 2-4 days for acute symptoms, with maximum benefit seen in the first week 3
- Critical warning: All muscle relaxant trials were ≤2 weeks duration; chronic use lacks evidence 5
Alternative Muscle Relaxant Options
If cyclobenzaprine is not tolerated or contraindicated:
- Tizanidine: First alternative with strong evidence (8 trials for acute pain), works through alpha-2 adrenergic agonism 5
- Methocarbamol or metaxalone: Acceptable alternatives without controlled substance classification 6
- Avoid carisoprodol: Despite efficacy, it is a controlled substance with substantial abuse potential and barbiturate-like effects 6
- Avoid diazepam: Particularly inappropriate due to increased risk of falls, sedation, and anticholinergic effects 5
Essential Non-Pharmacological Components
Physical therapy and range-of-motion exercises must be integrated with medication 3:
- Rest during acute phase
- Heat or cold application to reduce muscle spasm 3
- Gradual return to activity with proper body mechanics
Adjunctive Pharmacological Options
- NSAIDs: Equally effective as muscle relaxants for musculoskeletal pain with fewer adverse effects 6
- Antispasmodics (if visceral component suspected): Smooth muscle relaxants like mebeverine or alverine may provide benefit for abdominal pain, with 22% improvement over placebo 7, 8
Critical Safety Considerations
Central Nervous System Effects
- All muscle relaxants cause somnolence, fatigue, and lightheadedness with a relative risk of 2.04 for CNS adverse events compared to placebo 3
- Warn patients about impaired ability to drive or operate machinery 4
Anticholinergic Effects (Cyclobenzaprine)
- Dry mouth, drowsiness, confusion, urinary retention, and constipation are common 5
- Similar adverse effect profile to tricyclic antidepressants 5
Discontinuation Protocol
Taper slowly over 2-3 weeks after prolonged use to prevent withdrawal symptoms including malaise, nausea, and headache 5, 3. Abrupt discontinuation can cause significant withdrawal effects.
Special Populations
- Elderly patients: Strongly avoid muscle relaxants due to increased risk of falls, sedation, and anticholinergic effects 3. If absolutely necessary, use lower doses 3
- Hepatic impairment: Use cyclobenzaprine with caution in mild hepatic impairment starting with 5 mg dose; avoid in moderate to severe impairment 4
What NOT to Do
- Do not prescribe opioids for simple musculoskeletal abdominal pain 3
- Do not use baclofen for routine musculoskeletal pain; it is primarily for upper motor neuron spasticity 5
- Do not assume visceral pathology without first excluding abdominal wall pain with proper physical examination 1
- Do not order repeated costly investigations once abdominal wall pain is diagnosed, as this perpetuates patient anxiety 1