Q8: November 2019 PLAB 1 Exam Style Question
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A 68-year-old woman, who recently moved to the UK from India, presents to her general practitioner's clinic with a six-month history of generalized musculoskeletal pain involving her back, hips, and legs. She also describes progressive difficulty in walking and frequent falls over the last two months. She denies any other associated symptoms like fever, night sweats, or unexplained weight loss. She has no past medical history of note and is not on any medications.
Blood investigations show:
- Serum Calcium: 2.03 mmol/L (Normal 2.2 - 2.6 mmol/L)
- Serum Phosphate: 0.67 mmol/L (Normal 0.8 - 1.5 mmol/L)
- Alkaline Phosphatase (ALP): 270 U/L (Normal 30 - 130 U/L)
Given her symptoms and blood investigations, what is the single most likely diagnosis?
A. Paget's disease of bone
B. Osteomalacia
C. Multiple Myeloma
D. Hypoparathyroidism
E. Skeletal tuberculosis
Answer: B. Osteomalacia
Explanation
Diagnosis:
The most likely diagnosis in this case is osteomalacia, based on the patient's clinical symptoms and biochemical findings. The key findings include low serum calcium and phosphate levels combined with elevated alkaline phosphatase (ALP).
A. Paget's disease of bone:
In Paget's disease, ALP levels are usually markedly elevated, but calcium and phosphate levels tend to be within normal ranges. Moreover, Paget's often presents with localized bone pain rather than generalized musculoskeletal pain.
B. Osteomalacia:
This is the correct answer. The presentation of generalized bone pain, muscle weakness, and abnormal gait, along with low calcium and phosphate levels and a raised ALP, is most suggestive of osteomalacia.
C. Multiple Myeloma:
This is unlikely as there are no B-symptoms like fever, weight loss, or night sweats, and common lab findings like hypercalcemia are not present.
D. Hypoparathyroidism:
While hypoparathyroidism could cause low calcium levels, it would not explain the elevated ALP or the low phosphate levels.
E. Skeletal tuberculosis
Skeletal TB would be accompanied by other systemic symptoms such as fever, weight loss, and night sweats, which are absent in this case.
Clinical Takeaways:
1. Biochemical Markers: Low levels of calcium and phosphate along with elevated ALP are strong indicators of osteomalacia.
2. Investigations: Confirmatory investigations could include a Vitamin D level, parathyroid hormone (PTH) level, and X-rays of the affected bones.
3. Management: Vitamin D supplementation and correction of the underlying cause are the mainstays of treatment.
Summary:
Given the patient's generalized bone pain, muscle weakness, and abnormal biochemical markers, osteomalacia is the single most likely diagnosis. This condition may often be underdiagnosed and requires a high index of suspicion, especially in at-risk populations.
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