Looking in his medicine cabinet, a 45-year-old man with fever, nasal congestion, fatigue, and arthralgias finds a drug that was originally prescribed for his 15-year-old son’s acne. He comes to see his doctor after noticing he has been urinating more frequently than normal ever since taking this drug. Physical examination reveals dry mucous membranes. Blood tests reveal hypokalemia and a pH of 7.2. Urinalysis reveals elevated levels of glucose, protein, calcium, and phosphate. If this condition goes untreated, which of the following is the most likely long-term complication for this patient?
Diabetes insipidus
Diabetes mellitus
Osteomalacia
Osteopetrosis
Rickets
Correct answer
Osteomalacia
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correct answer: C
Seeking relief from the flu, this patient self-medicated with tetracycline, which was originally prescribed for his son’s acne vulgaris. Expired tetracycline is a known cause of Fanconi’s syndrome, a hereditary or acquired disorder of the proximal tubule of the kidney. This leads to defective transport of certain substrates, including glucose, amino acids, sodium, potassium, phosphate, uric acid, and bicarbonate. Characteristic findings include glucosuria, phosphaturia, proteinuria, polyuria, dehydration, hypercalciuria, and hypokalemia. Bicarbonate wasting can lead to renal tubular acidosis, while phosphate wasting can disrupt vitamin D metabolism and bone mineralization. This can result in rickets or impaired growth in children, and osteomalacia, osteoporosis, and pathologic fractures in adults.