What are the differential diagnoses and initial evaluation for shoulder cramping pain in a pregnant woman?

Shoulder Cramping Pain in Pregnancy: Differential Diagnoses and Initial Evaluation

The most critical differential diagnosis for shoulder pain in pregnancy is ruptured ectopic pregnancy with hemoperitoneum, which requires immediate ultrasound evaluation and surgical consultation, as this represents a life-threatening emergency. 1

Life-Threatening Differentials (Evaluate First)

Ruptured Ectopic Pregnancy

• Shoulder pain results from diaphragmatic irritation caused by intraperitoneal bleeding from a ruptured fallopian tube. 1
• Look for associated abdominal pain, vaginal bleeding, hemodynamic instability (tachycardia, hypotension), and syncope. 1
• Immediate pelvic ultrasound is mandatory to identify ectopic pregnancy and free fluid in the abdomen. 1
• This requires emergent surgical consultation for potential laparoscopy or laparotomy. 1

Acute Coronary Syndrome

• Shoulder pain can be a presenting symptom of ACS in pregnancy, particularly in women with risk factors including advanced maternal age, smoking, hypertension, hyperlipidemia, diabetes, or family history. 2
• ACS in pregnancy occurs at 3-6 per 100,000 deliveries and can present at any gestational stage, with increased risk peripartum. 2
• Look for chest pain (though may be atypical), dyspnea, diaphoresis, and ECG changes. 2
• Obtain ECG and troponin I immediately—elevated troponin indicates ischemic heart disease even in the presence of pre-eclampsia. 2
• Echocardiography should be performed urgently to evaluate for wall motion abnormalities. 2
• Spontaneous coronary artery dissection is more prevalent in pregnant than non-pregnant women, particularly around delivery and early postpartum. 2

Pulmonary Embolism

• PE presents with dyspnea (62%), pleuritic chest pain (55%), cough (24%), and may include shoulder pain as referred pain. 2
• Look for tachycardia, tachypnea, hypoxemia, and abnormal alveolar-arterial gradient (>15 mm Hg in 58% of confirmed PE). 2
• Risk factors include thrombophilia, pre-eclampsia, postpartum infection, and postpartum hemorrhage. 2
• Begin evaluation with chest radiograph, followed by bilateral lower extremity compression ultrasound. 2
• If ultrasound is negative and clinical suspicion remains high, proceed to CT pulmonary angiography or V/Q scan. 2

Aortic Dissection

• Aortic dissection is a critical differential for acute chest/shoulder pain in pregnancy, particularly in women with hypertension or connective tissue disorders. 2
• Look for severe, tearing chest or back pain radiating to the shoulder, pulse differentials between extremities, and blood pressure discrepancies. 2
• Immediate echocardiography is indicated for suspected dissection. 2

Musculoskeletal Differentials (Most Common, Non-Emergent)

Pregnancy-Related Musculoskeletal Pain

• Shoulder pain is among the common musculoskeletal complaints in pregnancy, though less frequent than low back pain (70.7%), back pain (43.5%), and hip pain (32.1%). 3
• Shoulder pain in pregnancy results from hormonal changes causing ligamentous laxity, weight gain, postural changes with increased lumbar lordosis, and anterior pelvic tilt. 4, 5
• Pain typically worsens in the third trimester compared to first and second trimesters. 3
• Look for mechanical pain patterns, absence of red flags, and normal vital signs. 6, 3

Rotator Cuff Pathology or Shoulder Trauma

• If there is history of trauma or mechanical shoulder symptoms, initial evaluation should include shoulder radiographs (AP, Grashey, and axillary or scapular Y views). 2
• Radiographs can identify fractures, dislocations, and gross bony abnormalities. 2
• Ultrasound with appropriate expertise is excellent for evaluating rotator cuff tears and biceps tendon pathology without radiation exposure. 2
• MRI without contrast can be used if ultrasound is non-diagnostic and soft tissue pathology is suspected. 2

Initial Evaluation Algorithm

Step 1: Rapid Assessment for Life-Threatening Causes

• Obtain vital signs immediately—fever, tachycardia, hypotension, or tachypnea indicate serious pathology. 2
• Ask about vaginal bleeding, abdominal pain, syncope, chest pain, dyspnea, and hemoptysis. 2, 1
• Perform focused physical examination looking for peritoneal signs, cardiac abnormalities, and respiratory distress. 2

Step 2: Immediate Testing Based on Clinical Presentation

• If vaginal bleeding + abdominal pain + shoulder pain: Obtain immediate pelvic ultrasound for ectopic pregnancy. 1
• If chest pain + dyspnea + shoulder pain: Obtain ECG, troponin, and chest radiograph. 2
• If isolated shoulder pain with mechanical features and normal vital signs: Consider musculoskeletal etiology. 6, 3

Step 3: Advanced Imaging When Indicated

• For suspected PE with negative lower extremity ultrasound, proceed to CT pulmonary angiography (preferred) or V/Q scan. 2
• For suspected rotator cuff pathology, use ultrasound first, then MRI without contrast if needed. 2
• Avoid delaying necessary imaging in pregnancy—maternal survival takes absolute priority. 2

Critical Management Pitfalls

• Never dismiss shoulder pain in pregnancy as purely musculoskeletal without first excluding life-threatening causes, particularly ruptured ectopic pregnancy and cardiovascular emergencies. 2, 1
• D-dimer has poor specificity in pregnancy (15% specificity, negative likelihood ratio 1.8) and should not be used to exclude PE. 2
• Do not delay imaging or intervention when serious pathology is suspected—radiation exposure concerns are secondary to maternal survival. 2
• Ergometrine given postpartum for bleeding can cause coronary vasospasm and ischemia presenting as shoulder pain. 2