Differential Diagnosis of Musculoskeletal Disorders
Cause:
- Metabolic
- Renal osteodystrophy
- Osteomalacia
- randomly distributed focal sites of intense activity = Looser zones = pseudofractures = Milkman fractures (most characteristic)
- Hyperparathyroidism
- focal intense uptake ← site of brown tumors
- Hyperthyroidism
→ rate of bone resorption >rate of bone formation (= decrease in bone mass)- hypercalcemia (occasionally)
- elevated alkaline phosphatase
- radiographically NOT visible
- susceptible to fracture
- Widespread bone lesions
- Diffuse skeletal metastases: prostate, breast, multiple myeloma, lymphoma, lung, bladder, colon, stomach (most frequent)
- Myelofibrosis / myelosclerosis
- Aplastic anemia, leukemia
- Waldenström macroglobulinemia
- Systemic mastocytosis
- Widespread Paget disease
- diffusely increased activity in bones: particularly prominent in axial skeleton, calvarium, mandible, costochondral junctions (= “rosary beading”), sternum (= “tie sternum”), long bones
- increased metaphyseal + periarticular activity
- increased bone-to-soft-tissue ratio
- “absent kidney” sign = little / no activity in kidneys but good visualization of urinary bladder
- femoral cortices become visible
- CAVE: scan may be interpreted as normal, particularly in patients with poor renal function!
mnemonic: NATI MAN
- Neoplasm
- Arthropathy
- Trauma
- Infection
- Metastasis
- Aseptic Necrosis
Long Segmental Diaphyseal Uptake 
- BILATERALLY SYMMETRIC
- Hypertrophic pulmonary osteoarthropathy
- Thigh / shin splints = mechanical enthesopathy
- Ribbing disease
- Engelmann disease = progressive diaphyseal dysplasia
- UNILATERAL
- Inadvertent arterial injection
- Melorheostosis
- Chronic venous stasis
- Osteogenesis imperfecta
- Vitamin A toxicity
- Osteomyelitis
- Paget disease
- Fibrous dysplasia
= radiotracer accumulation at periphery of bone lesion with little activity at its center
- Aneurysmal bone cyst
- Giant cell tumor
- Chondrosarcoma
- Telangiectatic osteosarcoma
= decreased radiotracer uptake
- Interruption of blood flow in local bone
= vessel trauma or vascular obstruction by thrombus / tumor- Early osteomyelitis
- Radiation therapy
- Posttraumatic aseptic necrosis
- Sickle cell crisis
- Replacement of bone by destructive process
- Metastases (most common cause): central axis skeleton >extremity, most commonly in carcinoma of kidney + lung + breast + multiple myeloma
- Primary bone tumor (exceptional)
mnemonic: HM RANT
- Histiocytosis X
- Multiple myeloma
- Renal cell carcinoma
- Anaplastic tumors (reticulum cell sarcoma)
- Neuroblastoma
- Thyroid carcinoma
Radionuclide Uptake in Benign Bone Lesions
- NO TRACER UPTAKE
- Bone island
- Osteopoikilosis
- Osteopathia striata
- Fibrous cortical defect
- Nonossifying fibroma
- INCREASED TRACER UPTAKE
- Fibrous dysplasia
- Paget disease
- Eosinophilic granuloma
- Melorheostosis
- Osteoid osteoma
- Enchondroma
- Exostosis