{
  "abstract": "A female in her 30s presented with a 6-month history of progressively worsening, dull aching pain in the right leg, which had begun to interfere with her daily activities. An X-ray performed at a private facility revealed bilateral transverse lucencies in the fibulae, raising suspicion of an underlying metabolic bone disease ( figure 1). Further evaluation showed corrected serum calcium 2.32 mmol/L (reference: 2.12–2.55), serum phosphorus 0.77 mmol/L (reference: 0.81–1.45), alkaline phosphatase 394 IU/L (reference: 30–130), 25-hydroxy vitamin D 60 nmol/L (reference: 75–250) and intact parathyroid hormone 4.8 pmol/L (reference: 1.6–6.9). Serum potassium was 2.7 mmol/L (reference: 3.5–5.0). Arterial blood gas analysis revealed a normal anion gap metabolic acidosis (pH 7.25 (reference: 7.35–7.45), HCO₃⁻ 11.8 mmol/L (reference: 22–26 mmol/L), PCO₂ 30 mm Hg (reference: 35–45 mm Hg), Na+ 141 mmol/L (reference: 135–145 mmol/L), Cl⁻ 117 mmol/L (reference: 98–107 mmol/L); calculated anion gap=13 mmol/L (reference: 8–16 mmol/L)). Simultaneous urine examination showed inappropriately alkaline urine (urine pH 7.5) in the setting of systemic acidosis, with no evidence of glucosuria. Twenty-four-hour urine collections demonstrated hypocitraturia (<0.2 mmol/day; reference: >1.7 mmol/day) and low-normal urinary calcium excretion (2.4 mmol/day; reference: <4 mmol/day). Spot urine electrolytes revealed sodium 72 mmol/L, potassium 37 mmol/L and chloride 88 mmol/L, giving a calculated urine anion gap of +21 mmol/L, consistent with impaired ammonium excretion. Taken together, these findings strongly supported the diagnosis of distal renal tubular acidosis (dRTA). Ultrasonography of the abdomen supported this diagnosis by revealing bilateral medullary nephrocalcinosis (figure 2). Skeletal survey revealed bilateral transverse lucencies in the distal ulnae and proximal femoral shafts, consistent with insufficiency fractures (figure 3). There was no history of trauma, joint pains, oral ulcers, dry eyes or mouth, or use of nephrotoxic medications such as Non -Steroidal Anti-Inflammatory Drugs (NSAIDs), amphotericin B or lithium. There was no history of similar symptoms, renal disease or skeletal deformities among family members. A comprehensive autoimmune workup, including antinuclear antibody, anti-Ro/SSA, anti-La/SSB and anti-dsDNA, was performed and returned negative, effectively ruling out systemic lupus erythematosus, Sjögren’s syndrome and other connective tissue disorders. Pure tone audiometry was normal, helping exclude syndromic forms of hereditary dRTA. In the absence of systemic, familial or autoimmune causes, the patient was ultimately diagnosed with idiopathic acquired dRTA. The patient was initiated on combined alkali therapy with potassium citrate (10 mL two times per day; each 5 mL providing 10 mEq citrate) and sodium bicarbonate 500 mg three times per day (6 mEq bicarbonate per tablet), delivering a total of approximately 60 mEq/day of bicarbonate equivalents. At the 3-month follow-up, serum bicarbonate, potassium and phosphate had all normalised. Serum alkaline phosphatase showed a partial improvement, decreasing to 178 IU/L (reference 30–130 IU/L). No further biochemical or radiological follow-up was possible, as the patient did not return after this visit.",
  "authors": [
    {
      "affiliations": [
        "Department of Endocrinology, Jawaharlal Nehru Medical College and Hospital, Aligarh, India"
      ],
      "name": "Ahmad Alam"
    },
    {
      "affiliations": [
        "Department of Endocrinology, Government Medical College Thiruvananthapuram, Thiruvananthapuram, India"
      ],
      "name": "Vijayakumar Karthik"
    }
  ],
  "title": "Bilateral pseudofractures and medullary nephrocalcinosis: diagnosing distal RTA",
  "uid": "1041e991-1e9c-5522-939a-a07e2e00a9f8"
}