What is the most likely cause of ambulatory dysfunction in a patient with worsening weakness, unintentional weight gain, and purple abdominal striae, taking prednisone (corticosteroid) 20mg daily?

Iatrogenic Cushing Syndrome

The most likely cause of this patient's ambulatory dysfunction is iatrogenic Cushing syndrome (option A), resulting from her self-escalated prednisone dose of 40 mg daily for 6 months, which has caused proximal muscle weakness (steroid myopathy) and the classic cushingoid features she displays. 1

Clinical Presentation Confirms Cushing Syndrome

This patient presents with the pathognomonic triad of hypercortisolism:

• Central obesity with weight gain (20 lb) - classic redistribution pattern 2
• Purple abdominal striae - wide purple striae are highly specific for Cushing syndrome 2
• Proximal muscle weakness - manifesting as inability to ambulate without walker assistance 1
• Buffalo hump (fat pad at posterior neck) - another hallmark of glucocorticoid excess 2

The FDA label explicitly warns that corticosteroids cause muscle wasting and proximal myopathy, particularly at doses exceeding physiologic replacement (>7.5 mg prednisone daily). 1 Her dose of 40 mg daily for 6 months far exceeds this threshold and directly causes the observed muscle weakness and ambulatory dysfunction.

Why Other Options Are Incorrect

Hyperparathyroidism (option B) would present with hypercalcemia, kidney stones, bone pain, and psychiatric symptoms - none of which are described. It does not cause purple striae, central obesity, or buffalo hump. 2

Osteoporosis (option C) is a consequence of Cushing syndrome, not the primary cause of her ambulatory dysfunction. While glucocorticoids do cause bone loss, her acute 6-week decline in ambulation is due to muscle weakness (steroid myopathy), not fractures. 1

Primary adrenal insufficiency (option D) would cause hypotension, weight loss, hyperpigmentation, and hyponatremia - the opposite of her presentation. Her chronic supraphysiologic prednisone use has suppressed her adrenal axis, not destroyed it. 3

Vitamin D deficiency (option E) causes osteomalacia with bone pain and proximal weakness, but does not explain the purple striae, central obesity, buffalo hump, or hypertension. 1

Immediate Management Priorities

Do NOT abruptly discontinue prednisone - the FDA label explicitly warns that abrupt cessation after prolonged use causes adrenal crisis due to HPA axis suppression. 1 Her 6-month course at 40 mg daily has certainly suppressed her endogenous cortisol production.

Gradual taper protocol:

• Reduce by approximately 25-33% every 1-2 weeks initially 3
• Once reaching physiologic doses (≤7.5 mg daily), taper more slowly over several weeks 4
• Monitor for adrenal insufficiency symptoms: extreme fatigue, hypotension, nausea, confusion 3

Baseline laboratory assessment:

• Morning (8 AM) serum cortisol and ACTH - expect both suppressed 3, 5
• Electrolytes (sodium, potassium, glucose) 3
• Consider 24-hour urinary free cortisol to document hypercortisolism 5, 6

Addressing the Underlying Problem

The rheumatoid arthritis pain must be managed differently:

• Consult rheumatology for disease-modifying antirheumatic drugs (DMARDs) 1
• Target prednisone dose should be ≤7.5 mg daily long-term to minimize complications 1
• Consider steroid-sparing agents to control her RA while tapering 1

Critical Patient Education

Stress-dose steroids during illness or surgery - she will require temporary dose increases (50-100 mg hydrocortisone equivalent) during physiologic stress for up to 12 months after complete discontinuation. 1

Medical alert identification - she should wear a bracelet indicating chronic steroid use and adrenal suppression risk. 3

Signs of adrenal crisis requiring emergency care:

• Severe weakness, confusion, persistent vomiting 3
• Severe abdominal pain, profound hypotension 3
• Treatment is IV hydrocortisone 100 mg immediately 3

Monitoring During Taper

Clinical surveillance every 2-4 weeks:

• Blood pressure (expect gradual normalization) 7
• Weight and striae appearance 2
• Proximal muscle strength assessment 1
• Morning cortisol levels to assess HPA axis recovery 4

Recovery timeline: HPA axis suppression may persist for 6-12 months after discontinuation of prolonged high-dose therapy. 1 Complete recovery of muscle strength may take weeks to months after cortisol normalization. 1

Long-Term Complications to Address

Even after successful taper, she remains at risk for:

• Osteoporosis - initiate calcium/vitamin D supplementation and bisphosphonate therapy 1
• Cardiovascular disease - persistent hypertension and metabolic abnormalities may require ongoing treatment 8, 7
• Persistent myopathy - physical therapy and gradual strength training once cortisol normalizes 1