Examination of the central nervous system revealed reduced power and tone in the lower limbs, and absent ankle and knee reflexes

A 24-year-old Jamaican painter and decorator was admitted with acute colicky central abdominal pain associated with vomiting. The only past history was that of a viral illness associated with a rash two weeks previously. On examination, he appeared pale. The heart rate was 110 beats/min and the blood pressure
140/90 mmHg. The abdomen was generally tender, but there was no guarding, and bowel sounds were infrequent. Examination of the central nervous system revealed reduced power and tone in the lower limbs, and absent ankle and knee reflexes. Investigations are shown.
Hb 10 g/dl WCC 7 109/l Platelets 170 109/l MCV 63 fl MCHC 28 g/dl Blood film (213) Urinary d-ALA 100 mmol/day (normal range 11–57 mmol/day) Sodium 134 mmol/l Potassium 3.2 mmol/l Bicarbonate 15 mmol/l Chloride 115 mmol/l Urea 7 mmol/l Creatinine 80 mol/l Calcium 2.32 mmol/l Albumin 40g/l Glucose 4 mmol/l CT of brain Normal

What is the diagnosis?
a. Sarcoidosis.
b. Acute intermittent porphyria.
c. Lead poisoning.
d. Arsenic poisoning.
e. Polyarteritis nodosa.

In a young man with abdominal pain, vomiting, neuropathy and anaemia, the most likely diagnosis is lead poisoning, although several other conditions may also cause the same symptoms (Table). The diagnosis is confirmed by measuring the serum lead concentration. A lead concentration above 4 mmol/l is toxic. Treatment is with D-penicillamine therapy. Acute lead poisoning is rare, but chronic poisoning may occur in scrap-metal workers or plumbers, in individuals ingesting water from lead pipes, in children ingesting old lead-based paint in the house, and painters and decorators. Lead interferes with haem and globin synthesis (see Answer 147). The effects are a microcytic anaemia and raised precursors of haem synthesis. The latter cause abdominal symptoms, autonomic and motor neuropathy which are identical to those seen in AIP. In both lead poisoning and AIP the -ALA is elevated; however, lead poisoning is differentiated from AIP by the relatively severe anaemia, basophilic stippling affecting the red cells and the elevated proto- and coproporphyrins. Basophilic stippling is caused by aggregates of RNA resulting from inhibition of the enzyme pyrimidine-5-nucleotidase. Other features include haemolytic anaemia, lead encephalopathy (which is characterized by a high CSF protein), a blue line on the gums, and dense metaphyseal bands at the end of long
bones in children (known as lead lines). Proximal RTA is recognized and comprises a hypokalaemic, hyperchloraemic acidosis, as well as loss of amino acids in the urine. Although sarcoidosis may be associated with abdominal pain and polyneuropathy and is more common in patients of Afro-Caribbean origin, there is no evidence of pulmonary symptoms, bone pain, iritis or hypercalcaemia. The raised ALA cannot be explained by sarcoidosis. Arsenic poisoning may affect patients working in some metal and glass production industries and patients who have deliberately or accidentally ingested certain rodenticides. It presents acutely with severe abdominal cramps and profuse diarrhoea. Chronic exposure usually presents with a painful peripheral neuropathy, hyperkeratosis, microcytic anaemia and white horizontal lines on the nails (Mee’s lines). Arsenic does not interfere with haem biosynthesis