What are the possible causes of left arm pain at the elbow and rest, associated bruises without trauma, and hypokalemia in a 39-year-old female?

Possible Causes of Left Arm Pain at Elbow with Bruising and Hypokalemia

This clinical presentation suggests hypokalemia-induced muscle weakness with secondary trauma from falls or muscle injury, though primary musculoskeletal pathology with coincidental hypokalemia must also be considered.

Primary Diagnostic Consideration: Hypokalemia-Related Manifestations

The potassium level of 2.8 mEq/L represents significant hypokalemia that can directly cause the presenting symptoms:

• Muscle weakness and pain are direct consequences of potassium depletion, as hypokalemia produces weakness, fatigue, and in advanced cases can lead to flaccid paralysis 1
• Spontaneous bruising may result from falls or trauma secondary to muscle weakness, or from direct muscle injury (rhabdomyolysis) associated with severe hypokalemia 2
• Hypokalemia can cause rhabdomyolysis, which would explain both arm pain and bruising without recalled trauma 2

Underlying Causes of Hypokalemia to Investigate

Renal Potassium Wasting

• Diuretic therapy is the most common cause of potassium deficit and should be the first consideration 3
• Primary or secondary hyperaldosteronism can cause inappropriate renal potassium loss 1
• Renal tubular disorders or potassium-losing nephropathy 1
• A urinary potassium excretion of 20 mEq or more per day with serum potassium less than 3.5 mEq/L suggests inappropriate renal potassium wasting 3

Gastrointestinal Losses

• Severe diarrhea, especially with vomiting, can rapidly deplete potassium 1
• Biliary tract or bowel fluid losses are usually identifiable by increased gastrointestinal output 3

Transcellular Shifts

• Insulin excess, alkalosis, or increased adrenergic activity can shift potassium intracellularly without total body depletion 2
• Certain medications affecting potassium distribution 2

Inadequate Intake

• Prolonged inadequate dietary potassium intake, though rarely the sole cause 1
• Patients on prolonged parenteral nutrition without adequate potassium replacement 1

Musculoskeletal Differential Diagnoses

While hypokalemia is the dominant finding, consider:

• Tendon or ligament injury at the elbow, though the absence of recalled trauma makes this less likely 4
• Muscle strain or contusion, which would typically require radiographic evaluation to exclude fracture 5, 6
• Occult fracture from a fall related to weakness, requiring plain radiographs as initial imaging 4, 5

Immediate Diagnostic Workup

Laboratory Evaluation

• Spot urine potassium and creatinine to calculate fractional excretion and determine if losses are renal or extrarenal 7
• Acid-base status assessment (serum bicarbonate, arterial blood gas if indicated) 3, 7
• Serum magnesium, as hypomagnesemia can perpetuate hypokalemia 8
• Creatine kinase to evaluate for rhabdomyolysis 2

Imaging

• Plain radiographs of the elbow are essential as the initial study to exclude fracture, dislocation, or other osseous pathology 4, 5, 6
• If radiographs are normal and soft tissue injury is suspected, MRI without contrast may be considered 6

Critical Clinical Pitfalls

• Do not assume bruising requires direct trauma—severe hypokalemia can cause muscle breakdown and weakness leading to falls or spontaneous muscle injury 2
• Mild hypokalemia (2.8 mEq/L) can represent significant total-body potassium depletion requiring substantial replacement, as extracellular fluid contains only 2% of total body potassium 2
• Chronic mild hypokalemia has serious long-term consequences including accelerated chronic kidney disease progression and increased mortality, warranting aggressive investigation and treatment 8
• Longer duration of symptoms before treatment is associated with worse outcomes 5

Treatment Priorities

• Potassium replacement is urgent given the level of 2.8 mEq/L and symptomatic presentation 1, 8
• Oral replacement is preferred if the patient has a functioning gastrointestinal tract and serum potassium is greater than 2.5 mEq/L 8, 9
• Identify and correct the underlying cause of hypokalemia to prevent recurrence 1, 3
• If diuretic-induced, consider dose reduction or addition of potassium-sparing agents 1, 3